This is a tutorial done by Happyroach over Soompi forums. I only included the relevant sections
I. Signing Up
II. Downloading Files
III. Redeeming Your Quick-Download Coupons
IV: Using Your Coupon
V. Download Capacities: How Fast and How Much You Can Download
I: Signing Up - Getting Your Own Account
The main benefit of having a Clubbox account is so you can download from protected Clubboxes (those that only allow members to download). To join boxes, skip to the bottom of this post.
1. Go here: http://client.clubbox.co.kr:8002/capp/join_abroad.cgi
2. Click this: 
3. Fill out the form.

If somehow you can't get to the next step (you get some internal service error, etc), refresh the page or go back and try again
4. Check where it says
and click this 
5. You should be brought back to Clubbox's homepage. Sign in with your ID+PW and you're set.
6. No, you don't have to fill in real information. Also, uncheck all the mailing options boxes if you don't want Clubbox/PDbox to email you.
II: Downloading
1. Make sure you're working with Internet Explorer. As much as I'd prefer to use Firefox, unfortunately, Clubbox only works with IE (and a few other IE-based browsers).
2. In your IE, go to Tools > Internet Options > Security > Trusted Sites > Sites > Add "https://clubbox.co.kr" > OK.
3. Install this: http://www.clubbox.co.kr/neo.fld/ClubboxSetup.exe
4. If you're at a certain Clubbox (http://clubbox.co.kr/blahblah), read on. If you only see a 1/4 screen window with a file link, skip to Step 6.
5. You see a list of files like the screencap I made below. Check the one(s) you want, and press the light blue button

6. You see a new window pop up. Press the big white button on the bottom.

7. You will now see this window below. Technically it should disappear within a second and start your Clubbox program, but sometimes the server gets busy and it doesn't respond.

What you should do if the window gets stubborn and doesn't go away:
Press Alt + left arrow, then Alt + right arrow. Your Clubbox download manager should pop up now.
8. And it looks like this (most of everything is in English, so you shouldn't have problems maneuvering around):

After your file starts downloading, the progress bar should move and show your download speed. CB regular downloads are capped at 55kb/s. There's a thing called download coupons which allows you to do certain amounts of quick downloads (+500kb/s).
9. Preferences. Go to the Config. tab and adjust for yourself. The tab is in English, so you shouldn't have any problems.
III: Redeeming Your Quick-Download Coupons
This is only available to people who signed up with CB and has an ID.
For every hour you leave your CB open, you get 10 mileage points. Once you reach 1000 points, you can qualify for a quick-download coupon
1. In your Clubbox window, go to the Mileage tab

2. You should be brought to a page displaying the available coupons you can "purchase" with your points. Choose whichever you feel like (and whichever you can afford). Do mind that the coupons expire in a certain period of time:

2GB: 5 days
5GB: 10 days
10GB: 15 days
30GB: 20 days
100GB: 60 days
300GB: 90 days
If you use up the n gigs before the n days pass, your coupon will expire early. If you don't use up your coupon, it'll still expire in n days
3. Confirmations: click OK
IV: Using Your Coupon
1. Click
instead of 
to queue a file to quick-download.
2. New window pops up:

3. Your box would look something like this:

Download speeds vary depending on your internet connection and file popularity. I have Comcast Cable in Northern California and my highest quick-download speeds are around 500k/s. I tried it on campus (UCB library) and got speeds around 1000k/s. People in Korea are known to get speeds around 5000k/s. So it really depends.
Word of advice:
If your normal download speed does not exceed 50k/s, don't use quick-download coupons. It's not gonna make things any faster. Read the FAQs to see why.
V. Download Capacities: How Fast and How Much You Can Download
As I mentioned in the quick-download topic, your download capacities depends on the kind of internet service you have and the status of your computer on your router if you are using a router.
1. Internet service:
- T1-T3: very good. Quick connects AND quick downloads. Abuse your coupons liberally. For me.
- Cable: very good as well, though not as good as T connections. Quick connects and quick downloads. Abuse your coupons on popular files.
- DSL: mediocre/crappy. 3.0Mbit > 1.5Mbit. I used to have excellent cable, so I totally spoiled myself with quick connects and high download speeds. Now I am stuck on 1.5Mbit SBC DSL, which is utter crap. So it's quite difficult to get files started, though once they start, they download at normal speed (~55k/s). Quick-downloads suck here as well, because with 1.5Mbit DSL, you can get as much as ~100k/s with quick download if you are lucky.
- Dial up: my sympathies are with you.
2. Router settings:
- DMZ host: if you do not care about being hacked or maliciously used, and you do not care for anyone else on the network, set yourself as the DMZ host. Your computer would download at the maximum capacity while all other computers on the network would suffer with near eternal 0%'s.
- Port forwarding: Clubbox uses TCP port 19101 for transfers, PDbox (very similar program) uses TCP ports 15000-15099. (source: wikipedia)
With optimal router settings, expect these download speeds:
- T1-T3: normal: 55-60k/s; quick: 1000-5000k/s
- cable: normal: 55k/s; quick: 500-800k/s
- 3.0Mbit DSL: normal: 55k/s; quick: N/A (I have yet to test this myself)
- 1.5Mbit DSL: normal: 55k/s; quick: ~100k/s (slow connects. Expect being stuck at 0% often)
- Dial up: 5k/s (slow connects as well)
Note: where you live often determines what kind of internet service you have or can get.
The speeds stated here are all based on people's experience living in the US.
- I think someone mentioned that speeds in Malaysia are capped at a maximum of 50k/s (correct me if I'm wrong).
- Speeds in Korea are the best (well, duh ;D). Tina and co. have reported speeds around 3000-5000k/s.
- Speeds in China are decent. Friends in Shanghai tell me they get 1000+k/s
- Speeds in Canada are good (at least for Lisa unni ;D). Normal downloads and around 300k/s for quick.
- Not sure about any other country. Inputs will be appreciated