Fit means either of the following: Someone who is physically 'fit' is someone who is in shape and exercise often...they are strong. An article of clothing that 'fits' means that this clothing embodies you nicely Finally, having angry 'fits' means to have a period of emotions filled with anger A "Suit" is an article of clothing worn predominantly in formal ocasions. Following "suit" means to follow someone quickly or to do what they had done. Finally, "suited" means that something is acceptable for or convenient.

Difficult to say without any context. If we are talking about clothes, 'fit' means it is the correct size and 'suits' means it looks good on you. But, these words can be used in other situations. For example, agreeing on a time to meet another person. Person 1: What time suits you? (= is good for you) Person 2: Sometime after 3 pm. Person 1: Ok, that doesn't fit my schedule ( = I have no space for that in my calendar; I don't have time then)