"I had played last year" vs. "I did play last year"

Fuad asked, "What is the difference between 'I had played last year' and 'I did play last year'?"

It's hard to explain how these sentences differ without more context, so I am going to add a little bit. Compare these three sentences:

1. Laura played soccer last year.
2. Laura had played soccer last year.
3. Laura did play soccer last year.

Sentence 1, with play in the simple past, means that during a period of time that started and ended last year, Laura played soccer. We don't know whether Laura played once or many times; that isn't clear from this sentence alone.

Sentence 2, with play in the past perfect, means that at a time last year, before something else happened, Laura played soccer. We don't know from this sentence what the later event was.

In sentence 3, did, the simple past of do, adds emphasis. The speaker is making a strong and definite statement about what Laura did last year.