Grammar 的 問 題

If you want to say you dont know how to use that kind of I.T. equipment called computer, then you should say 'I dont know how to use the computer."

Sometimes we use 'the' with a singular noun to mean the whole race.

As most computers are similar, I think the writer does not mean to say that he/she does not know how to use a particular computer.

By the way, computer is not an uncountable noun.

I don't know how to use a computer. (cause you don't mean a particular computer)

I don't know how to use the computer!

Computer is a uncountable item!
No need to add "s"

Maybe you say:

I am not very well to use the computer.