An infinitive is the word to + verb. For example, to see, to go and to eat are infinitives. A gerund is a verb + ing. For example, seeing, going and eating are gerunds.
When we put two verbs after each other in English, the second verb can be either:
1) an infinitive: to + (verb)
2) a gerund: (verb) + ing
However, some verbs can be followed by only to + (verb) and some verbs can only be followed by (verb) + ing. Unfortunately, there is no simple rule to know which one can follow a verb. So, you’ll need to memorize the rules for each verb.
Verbs such as want, ask, hope and learn can only be followed by to + (verb).
◆ I want to go skiing this winter.
◆ My mother asked me to buy some milk at the store.
◆ We hope to see you soon!
◆ Where did you learn to play the guitar?
Other examples of verbs that are only followed by to + (verb) are: agree, decide, promise and would like.
Verbs such as enjoy, look forward to, finish and suggest can only be followed by (verb) + ing.