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Looks like my reply disappeared, sorry!

Make sure the lens is the right way around, the groove around the lens should be closest to the face of the lens at the FRONT of the scope. The full moon is great target for testing things out.

Check the focal length of the lens by using it to project a distant light/scene on a shaded wall. you need to be able to focus the shoulder of the eyepiece both closer and further away than this. If you can't you may need to adjust the tube length.
10mm and 25mm will be fine but something like 6mm might work well for higher magnification. This is a good scope for larger objects like the moon, andromeda galaxy and wandering through the milky way in Cygnus, Cassiopiea and Perseus.

You can use very short eyepieces for smaller objects. I would suggest 4mm is probably as short as you want to go, or use a 2x or 3x barlow with your 10mm eyepiece for more comfortable viewing.