Question

when do we use 'to'?

Answer 1

'to' is simply a marker - a sign of the infinitive. So you use it to indicate that this is a verb in infinitive form.

For example:

• I love travel - here 'travel' is a noun
• I love to travel - now you use marker to specify that you love the action of travelling.

Usually you can use also the gerund instead of infinitive:

• I love travelling.