1. Open the Frame with Photoshop (The frame should be a .psd or .png file)
2. Now open the Picture you want to insert.
3. Using the Move Tool drag the picture onto the Frame.
4. Click Layer > Arrange > Send Backward.
5. You can see that now the Picture is inside the Frame. You can adjust the Picture to the Frame size (Use the Free Transform Tool or Press Ctrl + T).
6. You are done! Now save the File as PSD (or merge the layers and save as jpg).