To get rid of the widget just slide it out of the container. Widgets don’t contain major information. They just help shape how your data is presented. They may, however, contain some settings, but the real data will stay in your Posts or Pages. As for the Menus you want, make sure you have two menus created, any name you wish, for example, Main and TopBar.
Here is an example of a theme that supports two menus, https://take.ms/HrM9J. In this case, they are called Primary and Secondary, which is semi-arbitrarily decided by the theme author. In this screenshot, the Primary menu was created and called Blank, with nothing associated with it. Rather than deactivating the menu, this was easier.
If you are just going to create external links, then you’ll need to create a menu for each using the Links option under the menu area. If the widget you want to get rid of is the Custom Menu widget, then you’ll have a menu that you can reuse. If it is some other type of custom widget, and anything is possible, you may have to start over creating a menu item for each link.