The relative pronoun joka allows you to make more complicated sentences by adding subordinate clauses that give extra information about the main clause.
You can make verbs into the -nut form, which is called the active past participle. This form is the used for several different functions. Find out more!
The first of this series is the active present participle, also called the VA-participle. It's used to replace joka-sentences as well as että-sentences.
If you understand the basics of postpositions, this is the right place for you Learn about the inflection of postpositions in the mistä and mihin form!