I think you're mixing up your terms.
In ArcGIS, and I believe in most database management systems, "column" (or "field") means the vertical parts of a table, while "row" means the horizontal parts. More info: https://pro.arcgis.com/en/pro-app/latest/help/data/tables/tables-in-arcgis-pro.htm
"Joining two tables" means adding some or all columns of Table1 to Table2, based on the equalness of a column in both table. More info: https://pro.arcgis.com/en/pro-app/latest/tool-reference/data-management/add-join.htm
Based on your mixup, I think you might be interested in appending Table1 to Table2. This takes all rows of Table1 and copy/pastes them into Table2. More info: https://pro.arcgis.com/en/pro-app/2.9/tool-reference/data-management/append.htm
If you want to add new rows manually, it depends on whether you work with a pure table or a table with a geometry field (Shapefile or Feature Class).
For tables:
- open the attribute table, scroll down
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- click where it says "Click to add new row"
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- A new row gets created, you can input your values.
- Save your edits
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For Feature Classes:
- open the feature creation panel
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- in the panel, click on the feature template you would like to create. If you click on the arrow to the right, you can input the attributes of the feature.
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- Choose one of the geometry creation methods and draw your feature on the map. FInish by clicking on the button, pressing F2 or double-clicking.
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- Save your edits.
Have a great day!
Johannes