Hi,

Regarding the widgets available in the odoo, you can checkout this blog:  Widgets in Odoo

For adding default value for the fields, after adding the field click on the corresponding field, then in the left side of the screen you can see options to change the corresponding field attributes,in it there is option to add Default value for the field. 

Other option to add default value for a field by activating the developer mode is: How To Set Default Value For A Field in Odoo

Thanks