He should told me yesterday.
=> He should have told me yesterday.
See Learning English | BBC World Service
She could play the piano. <could = past>
=> COULD + bare infinitive
She can play the piano. <can = present>
Note that, bare infinitives lack tense, which is why could and can carry tense. There's this rule: only one verb per simple sentence can carry tense.
 Would (a modal, a modal auxiliary verb, modal auxiliary) is a type of auxiliary verb.
- You could do this right now (, if you wanted to). <conditional>
- You can do this right now. <permission>
- She can <present> type well, and she could <past> type well as/(when she was) a trainee.
sunny tomorrow, I might
go to the beach.
(Going to the beach is only a possibility) If
early, you can
see my mother before she leaves.
(It is possible for you to see my mother) http://www.eslbase.com/grammar/first-conditional
When we use will
in the result
clause of the first conditional, we are certain that something will happen. It is definite
. But we can use may
instead of will
. This means that the consequence is not certain. It is possible, but not definite
I'm not feeling very well. If it rains tomorrow, I’ll
stay at home.
I'm feeling fine and I've got a car. If it rains tomorrow, I might
stay at home, or I may
go shopping. I'll decide tomorrow.
Note: In the first conditional, there is no difference in meaning
. BBC World Service | Learning English | The Flatmates - Language Point 24