As a new player, understanding the best ways to go and win are difficult which is why what this page is here for.
As a new player, you may not know the best units so here are some tips.
1. Always upgrade your supply (bottom left)
2. Start by milking the first mission's reward (C Mamluk XV)
3. Earn some cash for promoting your future units.
When you reach Liberty Offensive, there will be new rewards like uncommon units (UC) and bronze keys. A useful tip is to milk those missions so that you can upgrade those uncommon units and put them into your squad.
If you followed the initial tips, then you should have enough money to promote those uncommon units.
If not, find missions with money rewards.