all my meshes are showing this lines, how can i get rid of them and why is this happening?
Try going into your quality settings and increasing the resolution scale - it looks like your editor is compensating to get a better framerate.
Did you leave the default playerstart there? If you have two starts, the character will spawn at the first.
Pull everything up to Epic and see if it still happens.
I did it and the lines are still there 
what could be the reason?
One more thing i put a player starter in my map and the player starts outside my map what could be the reason of that?
Everything is in epic the lines are little
Now, are those lines normal?
Well, I believe it has to do with downscaling and antialiasing. You could also try dropping in a Post process volume and tweaking the antialiasing settings there.
To the left in your editor, there should be a menu with things you can place in your level, There, select a Post Processing Volume and place it in your level. Look through its settings for two things:
Unbound - this should be a tick box. Tick it, and the volume will work anywhere in your level.
Antialiasing - this should be a dropdown with settings for FXAA, Temporal AA and None. Try fiddling around with it and see what works best.
How can indo that? Sorry am pretty much new at this
By the way thank you very much you’ve been very helpful
I got but now that i try to open the level again says failed to open because the map was saved with a newer version of the engine now what?
What version of the engine did you last open the map with?
4.6.1 Is the one i use
Did you ever open or save the map with 4.5 or 4.7?
No i’r never used 4.7 or .5
In that case, I’m unsure. Can you create a new map and see if the problem occurs again?
It occured again