I only know how to play blackjack and not the side bets so I will tell you the basics.
The main aim of blackjack is to hit 21 or a number below 21 provided that the dealer hits lowere than your number or above 21.
The dealer picks up a card for you and themselves. Then the dealer picks another card for you and themselves. This time the dealer reveals your card but not theirs.
The combination of your two cards can be 21or lower. Now you have to choose to hit which means pick another card or stand which means you are sure that the sum of dealers card is less than yours or more than 21. The dealer can draw more cards until they reach 17.
How to split and double down
When you have two similar cards like 2,2 or 3,3 or K, J or Q, J or K, K you will see the option of "split" (symbo shown in attachment) . If you choose to split your €1 bet will become €2. Now you have two hands which means two bets of €1. Now you will have to choose the double town feature which is in orange color and has symbol "2x". This also means you are going to hit. Now your bets are €1 and €2 if you choose to double down on one hand. If you double down on both hands your total bet becomes €4.