use of could/might in present context

In present context could and might are used as less postive versions of can and may. What does this mean.

It means that they are more tentative, but it is not true of ‘might’.

I can do that for you = ‘I am confident that I am able to do it’.
I could do that for you = ‘I can do that for you IF you will permit me’ or ‘I THINK I can do that for you’.

I might/may see you tomorrow– In spite of the efforts of many grammarians to perceive a difference because they think there must be one, the only difference is which of the two words the individual speaker habitually chooses.