Raid mission ground combat question ? keep failing with fine end in jail and ages to get back

[Bob The Spaceman]

So I have been looking for ground missions for a few days now, I found a base with missions eventually and took a few raid mission, level 3 as there were no level 0 ones at all in any of the bases ... so off I was walking towards the base where I have to kill all scavengers 2 shots later I was dead, okay try and do it again and seems I failed it, I am now fined ? okay so tried the second mission landed walked up guy turns around I put my shield on 2 shots and I'm dead, so here is my question please, I obviously am very crap at playing fps games, even tho I am top 500 in overwatch and have played division series for years now, So shooting npc's you need different guns for shields? and then swap to another gun to shoot the un shielded body, is there a tutorial on how to not get swarmed by 10 npc at once with 0 chance of killing anyone, and secondly how do you find low levels ground missions especially if you have been playing for years and you have rep with many of your bases you visit, where are they please anyone know, and how do you engineer your gear with out mats for do it ?