The -ing form of a verb can be used as a noun. In these cases in Spanish we use a noun or an infinitive:

Skiing can be a dangerous activity (Esquíar, El esquí ...)

• Used as a noun can be the subject, object, complement of a sentence or object of a preposition

Writing in English can be complecated (subject)

I hate writing compositions (object)

One of my hobbies is skiing (complement)

He is afraid of making a mistake (object of a preposition)

• We have to use the -ing form instead of an infinitive in the following cases:

1- After prepositions. The -ing form must be used when a verb comes after a preposition:

He walked away without looking back

John is good at cooking

I am tired of waiting for you

He is always talking about buying a new flat

 

2- We have to use the -ing form after certain verbs and expressions: avoid, be/get used to, can't help, can't stand, don't mind, enjoy, feel like, finish, imagine, look forward to, miss, practise, suggest.

I enjoy travelling

I feel like going for a walk

I avoided seeing him again

I don't mind getting a job abroad

She can't stand wearing gloves

The infinitive is the base form of a verb. It may be used with 'to' (the to-infinitive) or without (the base infinitive).

• Infinitive with or without 'to' 

The to-infinitive is used:

1. after certain verbs: want, promise, hope, learn, ask, refuse, manage, need, choose, offer, decide, persuade, deserve, plan, expect, wish, would like.
2. after the auxiliaries to be, to have to, and ought to
3. used with the structure: 'to be + adjective + to-infinitive'
4. With the structure: verb + object + to infinitive. The commonest verbs used in this construction are: advise, ask, expect, intend, invite, oblige, order, persuade, recommend, remind, teach, tell, want. He wanted me to go (Not: *He wanted that I go)
   

He didn't want to buy that shirt

I hope to see you again

Do you promise to visit me more often?

It is not easy to learn a foreign language

You have to follow the rules

He asked me to lend him some money 

The infinitive without "to" is used:

1. after most auxiliary verbs: can, could, may, might, must, shall, should, will, would
2. after the verbs: make and let: make/let + object + infinitive
3. after certain expressions: had better, would rather.

It might rain tomorrow

She lets her children stay up very late

They made him pay back all the money

I would rather go home by taxi