Know your fretboard
Learn the notes. Alright I do believe everyone knows the alphabet A B C D E F G. Also in guitar the name of the strings start that alphabet on a note made just for guitar standard tuning . or mandolin or ukulele standard tuning. Look at above charts this is for guitar. E A D G B E they don’t all start on an A note.. All of this is called the Chromatic scale. Lets look at above chart, see that arrow pointing to E String? That letter starts the alphabet at E. Before we go too far let me mention the word Accidentals…i know funny word but that is what it is called.
My version(simple) between E and F and between B and C there is no sharps between those two the rest is alphabet letter followed by an Accidental. look at charts.
example start at E …now E open string next is F first fret(no Accidental) followed by F# second fret… G then G# look at fret 7 see B then goes to C? No accidental…
Look at top chart see the second fret it has 2 notes on it. F# or Gb. Going up in pitch you name it sharp and if going down in pitch Gb.