Kailangan kong makipag-usap kay Juan sa bahay mamaya.

In Tagalog, many modifiers (like kailangan “need/necessary”) require the next word to be linked with the linker -ng. You take ko (the genitive form of “I”) and add -ng to link it to kailangan:
• ko + ng → kong
This is why you say kailangan kong rather than kailangan ko.

Makipag-usap means “to talk with” or “to have a conversation with.” It’s built from:
• the prefix makipag-, which signals a mutual or reciprocal action “to engage with,”
• plus the root usap (“talk/converse”).
Together they form an actor‑focus verb indicating you are actively conversing with someone.

Kay is the dative (to/for) marker used specifically before personal names and certain pronouns. It shows the person you’re directing the action toward.
• sa is a more general locative/dative marker for places or things.
• ni is the genitive marker (possession).
So makipag-usap kay Juan literally means “talk with Juan.”

• Mamaya means “later (today)” or “in a little while.”
• Bukas usually means “tomorrow.” (It can also mean “open,” but context distinguishes it.)
If you intend later today, use mamaya. If you mean tomorrow, switch to bukas.

After modal words like kailangan (“need”), Tagalog takes the root/infinitive form of the verb. You don’t conjugate for aspect there. If you remove kailangan, you can mark future with -um- or -mag-. For example:
• Makikipag-usap ako kay Juan mamaya sa bahay = “I will talk to Juan later at home.”

Yes. Kausapin (ka‑usap‑in) is the object‑focus form meaning “to talk to someone.”
• Kausapin ko si Juan = “I will talk to Juan” (Juan is the focus).
• Makipag-usap ako kay Juan = “I will converse with Juan” (the action/engagement is the focus).
Both are correct; the choice shifts subtle nuance in focus and emphasis.