Package it in a folder of the format Type_Name (e.g. Weapon_Gun, Script_HideNames, Gamemode_TeamDeathmatch) with at least a server.cs and description.txt file to appear in the Add-Ons menu. A mod with a client.cs file automatically executes when you start Blockland.
description.txt should be formatted with the title and author fields. Look at the ones in existing mods for an example.