@Solonius_Rex is correct. Negative Security Status is incurred for attacking other Capsuleers which affects your ability to travel freely in High Sec space. Tags for Security can only be gained in Low Sec from Clone Soldier NPC’s. Those Tags can also be bought from the Market or Public Contracts and are only good for repairing negative Security Status.
@Do_Little is correct and has posted a link that will help. Since you’re talking about mission running it’s your Minmatar Faction standing that’s messed up. You don’t have to go to Low Sec space to fix it. The only Tags used for Faction Standing increase is with Data Center Agents. Getting the required amount of Tags will take a long time, best to just purchase them from the Market.
Running the SoE level 1 Epic Arc won’t do you any good if you’re constantly being attacked by NPC Faction police. ‘The Plan’ is the easiest and fastest way to repair negative Faction standings…