Piece #A2 is background. You will place this piece right sides together (rst) to piece A1. Pin them in place to eliminate shifting. You will be sewing on the line that goes between piece 1 and 2, so make sure to leave a quarter inch seam allowance as shown in the photo below.
Once sewing is completed, set the seam with the iron, fold back the paper exposing the seam allowance.
If you have it use your add-a-quarter ruler and trim off any access fabric.
Flip block over from paper side to fabric and fold back the background piece. Press seam open. This is also when you hold your breath that you have added enough fabric to cover the shape drawn for piece #A2, my tip is to always go bigger than you think you need.
Use your add-a-quarter ruler and trim off any access fabrics from piece #A1.
My advise when paper piecing is go slow, but don't give up, it just might become a process you really end up enjoying.