This section will allow you to enable required modules. You will be allowed to use these modules in your Sales and Purchase, only after enabling here.
To activate the Modules, Go to Settings > Modules.
You can see the modules list here. By default, Quotes, Retail Invoices, Credit Notes and debit Notes were enabled. You can enable or disable Modules here.
To edit the modules, click on Edit button situated at the right side. Then check or uncheck the modules you wish to have and click Save.