to (as a preposition) is used to indicate location. (ex: I went TO the store. I talked TO her.) to (infinitive) is the basic form of a VERB (ex: to go, to talk) Also, I don't quite understand your second question... Are you asking the difference between the tenses or the difference between (I have work to do) and (I am doing work)?

1. I love / like TO STUDY / STUDYING grammar. 2. I enjoy STUDYING grammar. After some verbs (such as "love" or "like"), you can use an infinitive or a gerund. After some verbs (such as "enjoy"), you can use only the gerund. On the Web, you can find lists of verbs that take only the infinitive, only the gerund, and either the infinitive or gerund.

Here is something that I read that might help you: Sometimes the word "to" is just a substitute for the subject. a) I agreed TO go. = I agreed I go. As you can see, this canNOT be the situation in: b) I agreed TO the plan. That canNOT mean "I agreed I the plan." ***** I want TO eat. = I want I eat. (sign of the infinitive) I went TO school = I went I school??? No! Therefore, preposition.