3 steps

1. STEP 1 · DRAW THE WINDOWTake the Pen from the toolbar on the left, or press P, and click to place anchors round the shape you want · a circle, an arch, a letterform, anything closed. Click the first anchor again to close the loop (⏎ or a double-click do the same). Click and drag as you place an anchor and it comes out curved. Nothing is committed yet: every point stays draggable while the loop is live.
2. STEP 2 · PRESS ⧉ CLIPOn the pen’s bar above the canvas, beside ⬢ Fill. The loop becomes a shape layer · the window · and a picture goes inside it. If you already had a picture selected in Layers it is moved directly above the window and clipped to it, keeping the pose you gave it. If you had nothing selected the picker opens, and the picture you choose lands filling the window edge to edge. Everything outside the loop is masked off.
3. STEP 3 · REFRAME IT, OR GIVE IT BACKThe window and the picture are grouped, so dragging either moves both. To reframe: pick the PICTURE’s row in Layers and drag it, or scale it · it slides about behind the window and the window does not move. To change your mind, right-click the picture’s row and choose Release the clip: the picture comes back whole, and the window is an ordinary shape layer you can delete or keep. One press of undo takes the whole thing away.

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