Well.... "kind" is singular and "kinds" is plural. So you use them depending on how many examples you have.

"Kind of" means "somewhat," "sort of," "a little" etc. An example sentence would be "I kind of like pizza but I like pasta better." You can also use "kind of" as an answer. Eg. "Do you like pizza?" "Kind of." It can also be shortened to "Kinda." "Kinds of" means there are multiple types of something. This cannot be used alone and needs to be in a sentence. An example sentence would be, "There are all kinds of flowers." Meaning there isn't just one type of flower, there are many different types. I hope this helps a little!