"āp kā" is possessive and corresponds to "tumhārā"
"āp ko" is dative (used for the indirect object, with very few exceptions) and corresponds to "tum ko" and "tumheṁ"
"āp se" corresponds to "tum se" which is simply the pronoun plus postposition "se"
Verbs and sentences structures may require different postpositions like "ko" and "se" .
Just make sure to always use the right one.
"se" does not only mean "from" (e.g. "vah ghar se āyā") , it also can mean "together, with" (e.g. "maiṁ ne us se bāt kī") or "by" (e.g. gāṙī se āyā) , depending on the verb and sentence strcuture.
The pronouns in dative ("ko" case) have slightly special forms:
maiṁ : mujhe, mujhko, ("mere ko")
tū : tujhe, tujhko, ("tere ko")
vah : use, usko
yah : ise, isko
ham : hameṁ, hamko
tum : tumheṁ, tumko
The first form (mujhe...) is more elegant, the second one (mujhko...) more common, both formal and informal/colloquial, and the third one (mere ko...) uneducated, but still quite common.