You may find this useful: the -ing is referred to as the gerund in some cases. The rules are here: https://www.ef.com/wwen/english-resources/english-grammar/gerund/

If you are looking for information on how to spell words that end in -ing, look at: https://www.grammar.cl/Notes/Spelling_ING.htm

If you’re talking about doing something, then make sure you have some form of is/are/am before the verb with -ing, like “I am running” or “He is running.” If you want to talk about the verb, like “Running is fun” or “Studying is hard”, then add -ing to turn it into a noun of sorts.

Are you asking about spelling rules?