Then:
There are roughly two directions, based on b/s and C/S.
Namely:
1.webform
2.winform
Webform should learn basic html, javascript, and then ASP.NET technology.
Winform is to learn common controls and some development skills of Winform.
Finally: Of course, the database is indispensable, at least you must know the standard sql query statements. Database selection, SQL Server/Oracle/MySQL/SQLite, etc. They are all arbitrary, and each database is different. They are mainly divided into t-sql and sql-plus, and both webform and winform should be studied.
Ado.net and data display technology, gridview and so on.