Water cooling question

wasn't sure where to drop this...so:

I have a stupid water cooling question. Ive never used water in any of my rigs, so I have little knowledge on what im doing. My question is about compression fittings. When i read something like: "inside diameter of 1/4" and an outside diameter of 3/8..." The Eff? I was told to use the biggest tubing available and use compression fittings...Im looking at stuff like; 1/4 x 3/8 Compression Fittings, 1/4 x 3/8, 3/8 x 1/2 , 3/8 x 1/2,1/2 x 5/8, etc...and i have no clue what to buy

The system im playing around with in my head will involve 3 or so water blocks. 2 for the video cards, 1 for the CPU, and maybe one for the Gigabyte board. There will be a bay Reservoirs, 3 fan Radiator, pump, etc...

thanks for any info...im a n00bz