Bending strings is used to give the guitar a more personalized and harmonic quality. The technique is used mostly by lead guitar players but is also applied in all styles of playing. String bending and vibrato techniques are two large components in making up a guitar player’s style. The combination of these skills more or less defines a considerable part of what makes your playing different than the next guy.
Bending the strings far enough to reach a desired pitch is the goal. One of the keys is to use three fingers to bend the string, instead of just one finger. Use your third finger on the fret you're bending and place your first and second fingers on the frets behind it, and use the strength of all three fingers when you do a bend.
Fret the note on the 7th fret of the third string with your third finger. Your other finger should follow on the 6th and 5th fret. Our goal is to bend this note up one step (the equivalent of two frets) and then release the note to its original pitch. Before you do your first bend hit the note on the 9th fret, this will be your reference note. When you do your bend the goal is to make the tone of your bend “reach” the tone of the reference note. Repeat: hit your reference note, then immediately jump to the correct position and play a bend until to can consistently match the reference note.
The length you hold the bend, how quickly you release it and any vibrato you add to the bend will define a large part of playing your style. It’s good to just have fun and try doing a number of bends and releases to hear all the different sounds you can generate. Try bending the note before you strike it so you just hear the release, or try using a wide or narrow vibrato so act character and color to your bends.
Be patient you haven't used these muscles before, and is will take time to strengthen. Keep practicing, and you'll get the hang of it eventually.