Im working on the Bethesda tutorial. I tried to load the plug-in Vault74.esm so i could continue. when i looked for the interior cell i made (The copy of Vault 108a), it was gone.
Help....

Load it in the geck? And why is your mod an esm? It should be an esp file. Give us more details, this is a very bland explanation that could mean a million things.

Sounds to me like it's a load order issue.. might need to use FOMM to set your mod load order differently.

ok... i meant an esp. Im new to this

the weird thing is I have little I cant tell you, theres no error message, the interior cell i made just disappeared.
i created a plug in and copied Vault108a and renamed the copy Vault74, I worked on it, and when i loaded on the GECK the next day it Vault74 was gone.

Well then I would have to say that you did not save. Its as simple as that. If its not there from one load to the next you forgot to save and must redo it.

Or you did not set your ESP (plugin) file as 'Active Plugin' on the GECK loading screen.