I’m going to talk a little about standings and how they apply to PVE.
There are the main NPC “empires”, Amarr, Caldari, Gallente and Minmatar. Each of these empires has a set of NPC corporations, and the NPC corporations have agents.
You, the player, talk to these agents and run the missions they give you. As you successfully complete the missions, you gain “standing” with the agent and the NPC corporation they are part of. You also gain some standing with the empire that NPC corporation is part of, but at a lower rate. Once you standing has risen by a certain amount with the NPC corporation, you will gain access to higher level agents in that NPC corporation that have harder/higher level missions. Over time you work your way up to the higher level agents, and your standing with the empire also gradually climbs as well.
One detail to be aware of are the ‘storyline’ missions. When you complete a certain number of regular missions with an agent, you will receive a message from a different agent telling you they have a special mission for you. The rewards will be significantly better that the regular missions, but there is a catch. These special missions ask you to directly fight against NPC ships from one of the other main empires and when you do that your standing with the other empire will go down.
If your standing with an empire gets too low, their NPC navy will start attacking you, even in hisec. Concord will NOT protect you from this.
You can reject these storyline missions without any serious penalty to your standings.
Even without doing these storyline missions, you can lose standing with other empires. A little bit of lore needs to be mentioned here. Caldari and Gallente used to be a single empire but Caldari broke away. Caldari and Gallente are not good friends because of this. The same is true with Amarr and Minmatar.
There is a hidden alliance between Amarr and Caldari, and another hidden alliance between Gallente and Minmatar. If you are running missions for Amarr NPC corporations, you will gradually build up standing with the Amarr empire AND with the Caldari, but you will slowly lose standing with Minmatar and Gallente.
You can balance this out by switching around which NPC corporations you run missions for. Every empire has NPC stations with agents from the other empires, so no matter where you are in NPC empire space (all of hisec and losec and a very small amount of nulsec), you should be able to find agents for the other empires so you can keep your standing with all the empires from going too low.
Now another matter about missions. Loyalty Points (LP’s). Every NPC corporation has a “store” that sells stuff, ammunition, modules, whole ships, implants, blueprints for building stuff. You need LP’s to buy from an NPC corporation’s loyalty store, BUT each NPC corp has it’s own separate LP’s. If you run missions for NPC corp A, you will earn LP’s for corp A but those LP’s only work for corp A, those LP’s do not work in the store of NPC corp B. Most NPC corp loyalty points CANNOT be exchanged for loyalty points with a different NPC corp. Once you have earned LP’s with NPC corp A, you’re stuck with those points. There are a couple of NPC corps that can convert their LP’s but they are a special case and as a new player you’re not ready for their missions.
Not all NPC corp stores are equally good, they do not all sell the exact same items. Doing some research to look at what different NPC corp stores offer is useful. If you run a lot of missions for NPC corp A but their store doesn’t offer items you want, you might be better off running missions for NPC corp B where their store has items you do want.
Looking at the NPC corp store items in-game isn’t simple but there are some player made web sites that can be used to see what is in the store of each NPC corp. This isn’t something I do a lot personally, but here is a site I know that does this. Other players may be able to suggest other similar sites.
There are also skills you can train that improve the rewards you get from missions.