There are 3 types of telescopes:
1)refractor, uses lenses
2)reflector, uses mirrors
3)catadioptric, uses both

try this and practice doing this during the day time, it's easier.

get your eyepiece, the one with the highest number on it (# mm); this is your lowest power eyepiece, always use this first (wider view and easier to see where you're pointing it), and place it in your telescope.

next, use the focusing knob to focus on a target (a faraway tree, lamp post, etc.). once you have it focused, and if you want to get a closer look, get the next highest number eyepiece and refocus on the target. this is how you change magnification.
if you have a barlow lens (2x or 3x) this will also change the magnification by 2x or 3x without having to buy other eyepieces, although you can still buy more.
put it together in this order:
eyepiece-->barlow lens-->telescope

use the star diagnal for land viewing.

if you have a reflector telescope,
the open part of the telescope tube next to the focuser points to your target. focus it the same as above.

oh, and sometimes, with refractors, you might have to use the
45 degree or 90 degree diagnal to focus the telescope.

and google how to use a telescope. there's nice observing tips :D

hope this helps :D

oh, and check out the moon at night. it's a very nice target.
best time to observe the moon is when it's not full.
you gotta check out the 'terminator' (area on the moon where the light and darkness is separated.