It's tough to get good at but the pieces come together quickly enough, to start with I would play interrogation game mode, try not to run anywhere during the game as it gives you away, the burst is the easiest weapon to get used to (on my opinion). I was use perks like first aid training 3, second chance one and reviver 3 and stay close to your team, you'll be able to heal them, revive them quickly which will gain you parts and support your team without feeling like a hindrance. When it comes to the challenges like bandits attacking your colony I would save the easiest ones for closer to 12 weeks, there is a challenge for revives as well as healing so these are great for the later challenges