How to get a values from <input> tag?

Answer 1

Usually like this e.g.:
let in = document.querySelector("input");
console.log(in.value);

Different input types have different values and attributes though. You can find them all on MDN if you want more detailed information :)

Answer 2

You. can assign an id to the input, then do

document.getElementById(your id).value

to get the value.