So before we can use this method there's a few things we have to know.
First we need to learn the name of each string of the guitar, from the thickest (Low E) to the thinnest (High E).
The first string on the guitar, the low E string, will have to be in tune in order for this method to work properly. You can either do this by getting your guitar tuner, playing the same note on another already tuned instrument, using websites/apps that present the correct note etc.
This can be a bit tricky for a beginners at first, but when you get a hang of it everything becomes so much easier and you won't have to be dependent on a tuner. Take your time, there's no need to rush this things in the beginning. It's like riding a bike basically.
When you got the reference note and your low E string is in tune the rest immediately becomes much easier.
Place your finger on the 5th fret on the low E-string while picking both the low E string and the open A string (second string). If your guitar is tuned properly the note and the sound will be the same. If not, tune the A string until it does and use that low E string as a reference note.
This procedure is repeatedly on every string with 2 exceptions: the G string and the high E string.
G string: same procedure but with your finger placed on the 4th fret instead of the 5th.
High E string: Pick both the low E and the high E without your hands on the fretboard, also known as open notes.
Congratulations, you've just tuned your first guitar all by yourself! Doing this every time you'll pick up the guitar will not just make you an awesome tuner, but also help you with fretboard awareness and improving your ear.