I can't tell when to use the auxiliary verb do and when to use the be verb is are, I do not always use computer Is there any formula or skill to distinguish Why is I am not always using computer wrong

I can't tell when to use the auxiliary verb do and when to use the be verb is are, I do not always use computer Is there any formula or skill to distinguish Why is I am not always using computer wrong

In a nutshell
Do followed by verb be followed by adjective or verb ing
The verb "be + ing" means to be doing something