This is usually done by long tapping on the desktop (or in a panel or folder), and then selecting “Add item…”. Select the item type to continue.
When adding apps, the app drawer is launched. You can tap on an app and it will be added where you originally tapped. You may also add multiple items this way: long tap on a app, select “Add to launcher”, then repeat for each app you want to add.
Deleting an object is done through the item menu, which is usually displayed by long tapping on an item. Select the “Delete” entry and the object will be removed, except for panels and folders where a confirmation is requested before to proceed.