Noun-modifying clauses
the (thing) that …, the (person) who …
Plain form + Noun
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To describe a noun with a whole clause, put the clause in front of the noun, in the plain form: 母が作ったケーキ, "the cake (that) my mother made". There's no word for "that" or "who"; the position does the work.
The verb can be any plain form: past (見た映画, "the film I saw"), ている (話している人, "the person who's talking"), negative (わからない言葉, "words I don't understand").
The subject inside the clause usually takes が, not は: 私が住んでいる町, "the town I live in".
Polite forms (作りました) don't go in front of a noun. The politeness goes at the end of the whole sentence instead.
Examples
これは母が作ったケーキです。
This is a cake my mother made.
昨日見た映画は面白かった。
The film I saw yesterday was good.
あそこで話している人は誰ですか。
Who's the person talking over there?
私が住んでいる町は静かです。
The town I live in is quiet.
日本語がわかる人を探しています。
I'm looking for someone who understands Japanese.