Here's how it works:
* Base verb + "-ing" = Present participle
For example:
* walk (base verb) + -ing = walking (present participle)
* eat (base verb) + -ing = eating (present participle)
* play (base verb) + -ing = playing (present participle)
The present participle is then used with a form of the auxiliary verb "be" to create the progressive form:
* I am walking.
* She is eating.
* They are playing.
Keep in mind that there are some spelling changes when adding "-ing" to certain verbs, such as doubling the final consonant or dropping a silent "e."