mods don't work in server

[morgan2334]

in any of the mod packs when i am on the server no one can place any blocks that are not from vanilla minecraft please help

[plowmanplow]

Then your server is vanilla or your client has mods that the server does not have.

[planetguy]

This is probably because the server host is double-clicking the server jar, not using a script or command line. A Google search will tell them instructions on how to use a script.