Help a poor newbie, pic related is a desk, should I glue it all

>>1202541
Glue won't fill the gaps if that's what you're asking. You could glue it up then put several coats of high build poly on top to smooth it out.

sawdust mixed with glue can work if you dont mind spending time jamming it though those empty spaces

Use a countertop epoxy finish or a marine epoxy. Seal the back so it doesn't leak everywhere and pour it on to fill the gaps. Tint the epoxy reddish black if you like.
When it sets, sand smooth and apply your finish of choice.

>>1202541
I can't tell 100% but those look like pine pallet boards, not oak.
So you can't use that desk as a writing surface long term regardless, the pen would groove the wood and cause a rubbing effect on future writing. A common fix for this is to put a glass or acrylic plastic top on the desk, for which it doesn't matter.

Also, you need to plane, scrape, or sand that, the wood looks splintery af.
I second
>>1202547
Glue them together as is, then sand, then apply a fresh bead of glue to all the grooves and sweep your sanding dust across them