Guide to Find Nebula
If you have a name for a nebula you want to visit, that is a “RN xxx xxx” something, you can copy-paste that in the find object window (F3), then press “goto”. If that nebula exists in your SpaceEngine version, your camera will go there.
In general, you can disable stars, planets and other objects, leaving only nebulae enabled on the filters toolbar to the right, then use the Universe Map (F1) to locate nebulae all around the latest selected object.
Refer to tutorials in-game for a better description on what you can achieve with that map mode.
If it don’t say “object not found” you have to press Enter or Go to after pasting the object’s name. The F6 window is where you go to paste “URL” type location links (se://…).