Basic adding/subtracting
This is square one. Start here if you're just starting algebra.

Basic multiplying/dividing
The next square. After you've solved ten gadzillion of these, you're ready to tackle just about anything.

Basic adding/multiplying mixtures
After you figured out how to solve for x with basic adding, subtracting, multiplying and dividing, you're ready to come here.

Basic distributive law problems
Same as the basic adding/multiplying mixtures except we throw in the distributive law to make things a little more interesting. Hope you're not scared off by big numbers

Quadratic problems
You get to put it all together here: fractions, cross-multiplying, FOIL, distributive law, integer adding and multiplying. All the problems come with fully-detailed solutions.