Learning any instrument or lyrics requires practice. Every musician has at some point sat down and just practiced their craft. There are many different ways of learning and they all are going to have varying results depending on the individual.
I can only recommend that with music you start slowly and play parts of songs till you have them down by memory and then move on. Rather than overwhelming yourself by trying to learn the whole song at once. Makes sense?
The same thing goes for lyrics I reckon. Start with one verse or just the chorus.
Once you have it down by memory move on to the next part.
And once you have one song down, you approach the next song the same way.
So if you keep this up you will eventually end up w a repertoire of songs.

Regarding using notes and tabs while performing. I guess it's all about how well you can do it and how you want the performance to be perceived. Does your favourite performers use sheet music? Do you play genres/pieces of music where it's ok or even preferred to play w sheet music? There's really no right or wrong answer, only your own preference.

Bands and musicians spend a lot of time and money on getting their performances right. It takes a lot of rehearsing to play a 30 song set without any notes or sheet music. There aren't really any shortcuts when it comes to this.


Hope this helps!