Another way to call the present participle is -ing form, which is usual but it´s not its real name.
What are the uses of present participle?
Present participle is a very commom form in English, we use it to form the progressive tenses, the gerund forms, adjectives and some nouns. Look at the following examples:
Mary is waiting for her sister (Present progressive).
I was doing homework when my mom came (Past progressive).
Reading is a nice hobby (Noun).
You are a hardworking person (Adjective).
Rules to form the present participle.
Generally, we just need to add ing at the end of the verb, but sometimes it's necessary to follow some patterns.
1. Double the last consonant to one or two syllable verbs ending in a consonant + vowel + consonant if they have the stress in the last syllable.
Run - running
Stop - stopping
Swim - Swimming
2. Omit the vowel "e" at the end and add "ing".
Write - writing.
Practice - practicing.
3. Some verbs don't admit an ing form, for a complete list of these verbs you can go to this site.