* "There after" (two words): This is used as an adverb phrase meaning "after that" or "subsequently." For example: "He went to the store, and there after, he went home."
* "Thereafter" (one word): This is an adverb meaning "after that" or "from that time onward." For example: "The agreement was signed, and thereafter, the company began operations."
Which spelling you use depends on the context of your sentence and the meaning you want to convey.