Tune, tabs, notes or lead of a song is the melody part (other being harmony and rhythm).
Once you have learnt how to tune guitar and learnt basic timing/beat you can start to play notes on the fretboard. There is no easy way. You need to practice and practice by increasing the speed/tempo. You can get the piano notes of most of the songs online to practice. Slowly you should also start to feel the melody and try playing the tune just by listening. You will know when you play the right/wrong note by hearning what you play. I highly recommend using another instrument like harmonica (or a keyboard) to practice playing the melody, so that you can yourself decipher the melody. The first song you can play just by hearning it will be a big achievement. As an absolute beginner you will go through following stages:
Try playing these beginner tabs in the section > 5 beginner guitar tabs on the left
The seven notes or "swar" of the scale are Sa, Re, Ga, Ma, Pa, Dha, Ni. (This is same as Do, Re, Me, Fa, So, La, Te in western classical music). This is also known as sargam. These swar (notes) are used to make scale known as "saptak"