It is as Jamie said. Too many things happen now, then and were perfectly completed then...and we try to use tenses to explain the order in which they happened or happen. Labels for tenses may not help, but reading a lot and practicing simple sentences definitely will.
The cat.
The cat sleeps.
The cat sleeps on the mat every evening. (Routine occurence - simple Present Tense)
The cat slept.
The cat slept on the mat last night.(Past Tense: I can see proof of it now; she did not sleep on the couch)
The cat is sleeping. (I.e. not hunting or eating etc. Gerunds help with showing continuing activities/ Continuous Tenses)
The cat slept while the dog was barking. (Here you see two things happening as in Jamie's explanation)
First get these, then we can look at the Perfect Tenses in detail.