Xapian, MySqldb, and Sqlite

i want to make some database operations using python in ubuntu. I will implement searching function in tables in my database. I searched about how to do it. But i come across many different database apis, search engines etc.They are :

Xapian, MySqldb, and Sqlite

Although i read from official website, I cant understand what they are and what purpose they are used. I don't know which one i should use. Could you please explain them in your own simple words? And what is the difference of them?

Thanks in advance.