How can I built a sim from the vanilla game and export it?I haven't used any EPs but I have used some mods and CCs.

Any CC that was used with a sim will not export with that sim unless that CC came in a Sims 3 pack, you have never cleared your DCBackup, AND you are exporting your sim as a Sims 3 pack. (And, hopefully, are using CC that the creator is happy to have packaged with the sim. Check their policy. It's also courteous to provide a link with the credits even if the creator doesn't ask you to.) If any of that doesn't apply, it won't be packaged. This also means that anything in your Mods folder will not be packaged, so you will need to provide links for it. (And credit, of course.)

Effects of slider mods can transfer with the sim, but unless the one using the sim has the same sliders it can cause weird effects on changing appearance or aging up. I don't know about additional tattoo placements, but I would assume the same caveat applies.

If you don't mind packaging the sim as a Sims 3 pack, you can do that from the CAS screen which you also get access to from a mirror or dresser (or with Master Controller.) Poke around and you will find a button to export the sim.

It's just as easy if you've named the sim to go into your Saved Sims folder in your Documents Sims 3 folder, find a file with your sim's name, and share that with your list of CC that the sim was using. (And prevents your sim from bringing along things like the demon boots.) This will not bring any CC, so you will need to have links and credits for it unless the creator allows you to share it with the sim. And if you were planning to share your sim here, check the Creator Guidelines. (under the Create tab, at the far right.)

Edit to add: And if you are sharing your sim at MTS, you MUST share the sim file, not a Sims 3 pack. Other sites have different policies, so you will need to know the policy wherever you are planning to share it.)