First u need these things
1.2 lenses
2.Hot glue gun
3.Thick Black Paper
4.Black Tape (any kind)

Buy two magnifying glasses.the first should have a large diameter and less magnifying power(2X,or 3X).The second should have small diameter and large magnifying power(6X or 8X ,the larger the better).

Break the magnifing glasses to obtain the lenses.Break the magnifing glass carefully ,I broke a lens like this .

Roll the black paper to form 2 tubes ,the first should fit the larger lens and the second should be able to slide inside the first one.
Now the sum of the lengths of your 2 tubes should be more than the sum of their focal lengths.To figure out their focal lengths solve this equation-  

Focal Length(cm)=                25                 
                                       Magnifying power

Hot glue the lenses on to their corresponding tubes.Make sure the two tubes slide into each other (refer to pic).This is the most crucial step in the entire instructable.
TIP -While hot glueing make sure not much of the glue falls on the lens.This ruins the lens.

The image formed at small distances will be inverted.But for Astronomy it doesnt really matter whether the planet is upside down or not.This same design was used by Galileo until be built his own design which made upright view.
To calculate the magnifing power of the telescope:-
M=     focal length of front lens      
        focal length of second lens