Virtually you can derive two adjectival participles (present and past) from any imperfective verb and one (past) from any perfective verb. Verbs can be either direct or reflexive. Plus sometimes passive participles are possible.

Example:
учить - to teach
учащий - one, who teaches (present active a.p.)
учимый - one, who is being taught (present passive a.p.)
учивший - one, who taught (past active a.p.)
учёный - one, who was taught (past passive a.p.)

a.p.-s can be used as adjectives and as nouns (like if you add "one" in English). Rather often they become regular nouns but always decline as adjectives. For example "учёный" also means "scientist".