You have to have your guitar in standard tuning, which means concert pitch, which means the note "A" vibrates at 440 hertz.
If you don't have a guitar tuner, then you need to find another instrument, like a piano. I believe middle C on a piano is the same pitch as your 2nd string played at the first fret.
Or find a harmonica and tune to that, or simply buy a guitar tuner...they're cheap these days...going for as little as $10.
Or find a song where you're certain what key the song is in, and tune to that.
If you search the internet, I'm sure you can find tuning examples, so you'll know where your guitar should be..pitch wise.
Long before the advent of guitar tuners, I used to tune to the Byrds version of "I'll Feel A Whole Lot Better," because I knew it was in A.
If your guitar is in tune...no need to worry about how tight the strings are...it takes care of itself.