In Power BI Desktop, there is a feature to Enter Data. This is useful if you would like to add some ad-hoc data that does not come from a data source. For example, you could create a simple table with some columns and rows, and then use that as you would with other tables in Power BI.
To do this, in a Power BI Desktop project, select Enter Data:
This will open the Create Table screen:
From here, you can enter new columns, give these columns names, and enter in rows of data. You can also give the table a name, in this case, Orders:
Click Load to load the data to the Power BI desktop, or Edit to open the Edit Queries window. Here we will open the Edit queries window.
To add/remove/change the table and data, under Applied Steps, click the icon next to Source:
From here, the same window will open, allowing you to change the table: