Some in English are to do sth and some are doing sth Don t know when to use that?

To do sth means to do something, doing sth. Refers to being doing something.

Used to mess around with the finch to do something: used to do sth

Be used to doing sth

to do sth means to be ready to do something doing sth means to be done.

start to do sth.（begin / start to do sth.and sart doing sth

begin / start doing sth.start to do sth means "to start doing something", and to do sth means "to start doing something (and then do the previous thing)", with "potential possibility"; start doing sth means "to start doing something (to do another)" and has the meaning of "to actually do it".

Differences in specific use:

1.Doing is used when starting a long-term activity or starting a habit

In this case, start begin doing is mostly used to indicate the start of a longer or recurring activity).

how old were you when you first started playing the guitar?When did you start playing guitar?

2.begin, start is used in the continuous tense, and the following verb is infinitive

i was beginning to get angry.I started to get angry.

the plaster was starting to fall from the walls.The plaster on the walls began to peel off.

3.The infinitive form to do is often used when attempt, intend, begin, start are followed by verbs such as know, understand, and realize that indicate a state of mind or mental activity.

i begin to understand the truth。I began to understand the truth.

mary started to guess what is in the bag.Mary began to guess what was in the bag.

4.When the subject of the sentence is the object (when the subject of the sentence is the thing and not the person, start to do sth is used).

the ice started to melt.The ice began to melt.