properly match the Verb with the time expressed in the sentence, when we say time, we mean the present, past, and future.

present tense: subject + -ING form of the verb

ex. *Single subject: I am typing. She is sitting.
*Plural subject: They are reading.

past tense: subject + past form of the verb
*past form of the verb = simple form + D or ED, or other form.
(ex. dive=>dived, learn=>learned, eat=>ate.)

future tense: WILL, WOULD, SHALL, SHOULD + simple form of the verb.

Use WILL/WOULD if time is sure to come;
SHALL SHOULD if time is not certain to come.

Other basic rules in the English grammar:

Verb be - AM, I, IS, WAS, WERE. DO, DOES, & DID. HAS, HAVE, HAD, these are all used with the SIMPLE FORM OF THE VERB

any more? :-)