When I was studying grammar, I learned that when we want to use a verb in its 'infinitive form' at the beginning of a sentence, we must use it in its 'gerund form', otherwise, if I used 'to' at the beginning of the sentence the verb wouldn't be in its 'infinitive form' because 'to' would be a preposition. I'm gonna give an example for you guys to understand better what I mean.
"Reading a little bit every day is an awesome activity". (Even though the verb is in the 'gerund', it means 'infinitive'.) [ Is this correct? ]
"To read a little bit every day is an awesome activity". (the word 'to' in this sentence doesn't put the verb 'read' in its 'infinitive form' because 'to' works as a preposition in this case.) [ Is this correct? ]
So, my question is: Must I always put the verb in its 'gerund form' to mean 'infinitive' at the beginning of a sentence or can I use both forms meaning the same? And is there any grammar rule which explains that?