Mag- is used with actor-focus verbs, meaning the actor of the sentence is marked with ang (for nouns), si (for names), or ang pronouns (ako, ka, siya, tayo, kayo, kami, sila). Krizia is correct about how to conjugate mag- verbs into the infinitive (mag-), completed (nag-), continuous (nag+first syllable of root), and contemplated (mag+first syllable of root) aspects.

Pag- is most often used to create what's called a gerund, or a verb that functions as a noun. These words should be understood as "the act of ____". For example, paglakad [walking] or pagmamaneho [driving]. As you can see, the second example has a reduplication of the first syllable of "maneho", which occurs because this is a mag- verb. Um- verbs do not have reduplications when a pag- prefix is added to them to create a gerund. Also, it's good to know that pag- can also appear as pagka- (used to create a noun from an adjective root) and pag- -an, which implies reciprocity with mag- -an verbs like maghalikan (to kiss each other) or pag-usapan (the act of discussing with each other).

Concerning the rest of the affixes covered by "etc", there are over 60 of them in Tagalog. The good news is that most of them follow a similar pattern of reduplication and once you learn their functions, you can understand any root that uses them more easily. Plus, only 10-15 are generally used in conversational Tagalog, so you won't be required to learn all of them before you can have a meaningful conversation.

If you'd like more info on other affixes, feel free to message me and/or schedule a session to spend more time on Tagalog grammar. Maraming salamat!