If you look at your personal information it will say what the next requirement is to level. If it says "mission", simply clear all waypoints and you'll be pointed to where you will get the next mission. If it doesn't, jump out of your current system and back in.

There are more missions from where you are btw.

SP can mean Single Player, where did you see it?

SP can also mean "spelling". In that case you see it together with a question mark next to an oddly looking word.

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"In all likelihood you're going to die out there. We're all going to die out there, but none of us needs to be reminded of that fact. So you die, you never existed." - Lt. Cmdr. 'Angel' Devereaux

To get the right answer to your question...this post would have to be on the spoiler forum.

Word of advice, after Tobias gives you money to buy a new ship, don't by the Freighter. A mission or two down the road, you need to do a race, and you wont be able to do it in a Freighter. Buy a Fighter.