Make sure the created custom module is present in the addons folder.( eg:/opt/odoo10/odoo/addons in Ubuntu). Now start the server from the terminal using the following command:

./odoo-bin

then login as admin user and activate developer mode. Then goto the 'Apps' menu and click "Update apps list" option. 

Then remove the "Apps" filter from the filter box and verify if your module is appearing. If yes Go ahead and install it.

Note: Make sure you have the below line in your __manifest__.py file. The module created from ./odoo-bin scaffold <module name> <where to put it> won't have these lines in its __manifest__.py. So check that also.

'demo': [        'demo/demo.xml',    ],
 'installable': True, 
 'application': False,
 'auto_install': False,
 'qweb': [],    }