How to Practice SQL commands and how to work with DataBases at home?

It depends on what your goal is. Are you just trying to practice SQL for creating web apps? Or are you trying to practice running a server like a DBA and focus on databasing? If it's just to practice SQL, download SQLite. If you're interested in really digging into databases, then download either MySQL, SQL Server, or PostgreSQL and practice setting it up. Just pick one that sticks out to you, and go with it.

If you are just wanting to practice simple queries, then model a business problem (think, for example, a warehouse that may have tons of inventory and customers with login names, or a hotel that has to keep track of guests, rooms, staff, and so on), and try to model the data for that problem. Once you have 6-7 tables of information, try to practice querying information across those tables. Whenever you're working with Databases, always think about how you want the data returned (i.e. the format, the order that the information's displayed in, etc.).

If you're really digging into databases, then practice what I just mentioned, but also look into setting up different roles for different users. For example, if you were to go with the hotel model, you'd want to have different DB accounts that have access to different tables. A manager may have access to the table with all of the employee's salaries, while the staff would not have access to that information.