Learn algebra by progressing in gentle steps from basic pre-algebra concepts to complex and demanding equations. These lessons and practice opportunities are both a useful tool to assist students in school, and a fun and rewarding exercise for all.
For some, and for the early categories presented on this website, there will be immediate success: the concepts will be known, the problems “easy” to solve, and the About sections, which explain the concepts and the methods of solution, unnecessary. But, as you progress through the levels, you will most likely reach a point where help will be needed to even understand what is being asked (go to the About) and practice will be needed to master the concepts being presented. At that point, it will be very helpful if those earlier concepts are so well ingrained that it is only the new concepts that require attention. Therefore, it is recommended that, although “easy”, those early subjects be practiced adequately to provide a high degree of comfort and competence.
When you do reach the unknown, study the About carefully (or, alternatively, read your textbook!). Even so, your answers will most likely often be met with “Sorry”. At this juncture, you may immediately try, on your own, to see if you can figure out where you went wrong; perhaps you just made a simple arithmetic or sign mistake. If you get a wrong answer the second try also, you can study the worked-out solution given (usually — a few categories of problem don't have these yet). Then you can go back and try again. Or you can go on to the next problem and hope for the best — that, with more and more problems, eventually you will acquire that degree of care and exactitude needed for correct algebraic manipulations. You need not fear that you will run out of problems — this is an endlessly-generating problem machine.
But above all, have fun, and remember that “practice makes perfect”.