There are 3 basic types of magazines in Airsoft, lo-cap, mid-cap and hi-cap. The Lo-cap magazines are low capacity (generally 25-35 BBs) single line of BB spring feed types. If these have the same capacity as the 'real steel' equivalent can also be known as real-caps and are favoured by people that want that bit more authenticity in their airsoft. These are fed by pushing BBs direct into the feed tube. Mid-caps have a medium capacity (generally 100 BBs or so) with a single spring feed line of BBs too. These are also fed by pushing BBs into the feed tube, you can save time by using speedloaders on both of these types.
Hi-caps get a little more complicated, they have a minimum of 190 BB capacity upto 1000 BBs in the really large standard mags or 3-5000 in the big box mags. The hi cap magazine works by winding up a spring which then actuates a feed mechanism to push BBs from a large BB reservoir up through to the AEG, in normal AEG mag hi caps this is done by winding a cog on the bottom of the magazine. In use this means you fill you magazine reservoir with BBs through a small door or slider usually on top of the magazine, you then wind your magazine via the cog (or on the Lonex mags via the pull cord), you will see the BBs arrive at the top of the feed tube, keep winding, you will feel the mechanism get tighter until you hear the spring slip slightly inside the mag, depending on the magazine capacity this should be able to empty the entire magazine without another wind. 99% of hi cap magazines work the same way, even the big electric box mags only use the electric motor to turn the first cog and charge the spring for you...
First off... CHECK YOUR BBS!! I cannot stress this enough! DO NOT USE POUND SHOP BBS!! Next time you see these take a look at them, cheap BBs have mold marks, nipples and are not properly round. These can kill your shiney new AEG! I have had brand new AEGs come in for repairs costing almost as much as the rifle was new just because they used crap BBs.
There are many different types and weights of BBs. Different weights work differently with different power BB guns and you can also get both illuminous and biodegradable types.
0.12g BBs work best for the basic electric BB guns, low power stuff with a low range.
0.2g Is the standard for all 'Skirmish Ready' BB guns & AEGs these are the minimum you should be looking at.
0.25g Can work better for some AEGs and GBB pistols & rifles.
0.28-0.3g This is now getting towards sniper rifle territory.
Generally the higher the power rifle the heavier weight BBs you should be using, all the way up to 0.4g I've heard being used in the field. If your BBs are curving off earlier that you think they should and the hopup is at a minimum heavier BBs are one of the cheapest and easiest things to try that could provide a significant improvement to your shooting.
Biodegradable BBs can be a solution to picking up BBs from lying around in your garden just be aware of your ammo, Bios can swell up over time and if they are not perfectly round they can cause jamming and inaccuracy problems