Start up with some simple exercises so your fingers will get used and gain strength, I wouldn't worry about learning songs just yet if u havent held a string instrument before.
You can find tons of exercise licks on google or you can just do the basic
1-2-3-4-3-2-1
or
1-3-2-4-2-3-1
or
1----2----3----4---
---3----4----1----2
Play them starting from the 4th string moving down the strings and advancing 1 fret every time u get to the last string until you get to the end of the fretboard. Try to play always as fast as you can while still maintaining a good sound and tempo. After a few times repeating this you will feel the difference on your fingers almost instantly.