Hi Peter, welcome to the forum. It can be a little difficult for a new reader to find the “getting started” material on this combined wiki and forum. Just a note on this thread, “updating” is the process of updating an existing /e/ system with its new version.
So let me first point you to:
/e/ Install page Samsung Galaxy S5 LTE International
You will see in the install page that we use sideload in two contexts. We use sideload with TWRP, here is their FAQ TWRP - FAQ - ADB Sideload.
As mentioned there, sideload is a feature of ADB so here is a rather heavy duty authoritative page on ADB
A brief interweb search for adb + sideload produced this. This tutorial is quite thorough, so a little bedtime reading there might be informative - but only for general understanding, always use the /e/ documentation to perform your install!
(I am guessing you may be from the USA, in which case it might be worth searching for “USA” in threads in our wiki, in case you get issues peculiar to USA carriers and their cartel which is well reinforced by Google.)
Edit. I provided that install page from your klte identification. Please be absolutely clear you have correctly identified your device before you proceed.