A seed keyword is the main, short-tail topic (usually 1-2 words) that describes what you do. It's the starting point for finding the specific phrases (long-tail keywords) people actually type into search bars.
Search intent is the "why" behind a search. Is the user looking for information (How-to), looking to buy (Commercial), or looking for a specific website (Navigational)? Matching your content to intent is key to ranking.
Focus on one primary keyword per piece of content, and 3-5 secondary (LSI) keywords that are closely related. Trying to rank for too many unrelated terms confuses search algorithms.