Have you booked bags to go in the hold? If so, put all your liquids in there.
At security you will first need to scan your boarding pass to enter security area. Most people have this on their phone.
At security, you will need to put everything in a tray. If you have electronics (e.g. iPads) or electronics, lay them out in the tray, don't pile things on top of them. You'll have to make sure your pockets are empty and put your jacket/scarf under n a tray (you may need multiple trays). Pay attention to signs in the security area, some airports might ask you to remove a belt or shoes. Confusingly for now, some airports are trialling scanners that don't require you to take everything out of your bags, but there will be signs. If you do have liquids in your hand luggage, they need to be in 20cm x 20cm clear bag.
If you have hand luggage, read their cabin bag rules carefully. Not all airlines are the same. Easyjet snd Ryanair have strict rules about what you can take on for free (the 'free' bag should go under the seat) and they often check these while you are boarding. A handbag is included in your cabin bag, it's not a separate item.
The airport screens will tell you what number your gate is and when to go to the gate. Your boarding pass should tell you when the gate is closing. If you have checked in luggage you will need your photo id when you are boarding the plane.
Once on the plane, quickly pop any cases in the overhead lockers, small bag under your seat and take your seat. You shouldn't put coats etc. in the overhead, space is at a premium, and for Ryanair or easyjet they're just for bags you have paid extra for.