Hi Ross,

to IceInSpace!
The "small eyepiece" as you call it, is called the "finderscope". It's usually something like a 6x30 on those small telescopes (6x magnification, 30mm objective diameter).
You use the finderscope as a low-power "finder" to find the object you're interested in, and then look through the main telescope to get a more magnified view.
The 2 eyepieces you have (12.5mm and 20mm) will give you magnifications of 72x and 45x respectively.
If you use the 2x barlow in conjunction with those eyepieces, it effectively makes the 12.5mm a 6mm eyepiece, and the 20mm a 10mm, giving you magnifications of 150x and 90x, respectively.
The 1.5x erecting eyepiece is a waste of space, you'll likely never use it.
Have a look at the following 2 reviews here on IceInSpace, of 2 similar small scopes. Some of the learnings there might help you with your scope:
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http://www.iceinspace.com.au/index.p...41,358,0,0,1,0
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http://www.iceinspace.com.au/index.p...41,362,0,0,1,0
You will probably need to align the finderscope so that what you point it at, matches what you see in the eyepiece. Do this during the day, on a far-away mountain or street-light. It won't work on close obejcts as you won't be able to bring it to focus.
Once you can see a street light or similar in your eyepiece, adjust the finderscope until the same object is in the middle of the crosshairs.
The moon will be up tonight - put in the 20mm eyepiece, use the finderscope to locate the moon, and then look through the main eyepiece. You will most likely need to focus (rotating the knobs backwards/forwards) until you see sharp detail.
You can then try the 12.5mm eyepiece, and then the 20mm + 2x barlow, and then the 12.5m + 2x barlow. With each increase in magnification, you'll see a closer-up view but it will also get harder to focus and more "blurry" looking when the conditions are not good.
Anyway give this a try and let us know tonight how you go.
Also point it at the brightest "star" that will be directly overhead shortly after sunset. That's Jupiter. You should see a bright ball and 4 bright moons nearby.
I hope this helps, Keep asking questions!