That means that the barrel will hold 2ml of whatever. The 21ga 1 1/2" part means that the needle is a 21 gauge and one and a half inches long. You should be buying the syringes with needles attached (2ml or 3ml barrel with a 21ga-23ga 1" needle) then a pack of needles only in whatever size you will be pinning with. Swap the needle out after drawing so you always pin with a fresh needle. 23ga 1.5" for glutes and 1" for anywhere else should work nicely
Arnolds first off you should always make an intro to the community so that we can give you a proper welcome. Second you should review the rules. http://musclegurus.to/content/rules-and-guidelines then you would know I edited your post for discussing sources in open forum.
Your best course of action my brotha is to make that intro, and some friends. Then you could ask them through pm where's the best place to get syringes from. To answer your question I prefer a 3ml syringe with a 23g 1.5 inch needle for injecting glutes and using a 20g needle for drawing in out of the vial. If your planning on running a cycle you should get active here, post up your stats and cycle history, lay out your cycle plans, and let these guys hash you out the perfect cycle for great gains and safety.
both ways work fine. by the way OP what are you running? FYI in case you didn't know,the bigger the number (eg 25g, 27g) the thinner the needle (hurts less, less scaring). as Dolf said, 3ml syringe 23g 1.5 inch needles will work great.