A computer chess engine obviously shows or plays the best move according to its strength. But in accordance to your improvement in chess given the fact you are a beginner, playing against the highest strength computer might not help you to have the best results. Chess from human point of view and computers point of view are very much different though obviously the rules are same.
As you are a beginner let me explain you how computer thinks and how beginners should.
A chess engine plays its best move, by calculating thousands of positions, and many variations from a single position. All it does is Math and because it is a computer it does it quick and accurate. But beginners can't do that. It is needed to learn the various concepts and ideas of chess to understand a particular position and your improvement in chess depends on how well you understand a particular position.
Let's say you are playing against computer and you end up in a bad position so you take back your moves and make other moves, and then again somewhere end up in a bad position. This does not help you to understand what is going wrong in your chess or how can u improve or what is your actual strength, because how much ever you try, you end up in bad positions because obviously the strength of the engine is so high up to the level of GrandMaster or even higher.
Use your chess engine to analyze your game after you finish it. Playing games of 15:10 time control is good for beginners, do no go into blitz now but a couple of games now and then is fine for fun. Its good for you to play long time control games because there you have more time to think and understand positions occurring from it. You will have time to think of a proper plan which you think is best for a position and then you can make your move accordingly. This also helps in analysis after the game. While analyzing, when chess engine shows some other moves/variation as a better one.. check that line(variation) out completely and there you can find what the plan of the computer was and how was it different from your plan for that particular position.
Check this great article, it helps you with various aspects of chess and helps you plan your study in chess from the level of beginners to Advanced. :)