Fixed Savings pays a fixed rate for a term of 1, 3, 6, or 12 months. Your funds stay in for the term, and interest is paid when it ends.
You choose the asset and the term, and each combination has its own rate. Your rate is locked in when you start and doesn't change until the term ends.
The app shows your rate as APR, your fixed yearly rate. For example, 1,000 USDC for 12 months at 8% APR earns 80 USDC.
When the term ends, your funds and interest can start a new term automatically. See How do I manage my Fixed Savings?