You can perform database queries through the self._cr.execute method:

self._cr.execute("SELECT id, name, date_release FROM library_book WHERE name ilike %s", ('%odoo%',))
data = self._cr.fetchall()
print(data)

Output:
[(7, 'Odoo basics', datetime.date(2018, 2, 15)), (8, 'Odoo 11 Development Cookbook', datetime.date(2018, 2, 15)), (1, 'Odoo 12 Development Cookbook', datetime.date(2019, 2, 13))]

The result of the query will be in the format of a list of tuples. The data in the tuples will be in the same sequence as the fields in the query. If you want to fetch data in dictionary format, you can use the dictfetchall() method. Take a look at the following example:

self._cr.execute("SELECT id, name, date_release FROM library_book WHERE name ilike %s", ('%odoo%',))
data = self._cr.dictfetchall()
print(data)

Output:
[{'id': 7, 'name': 'Odoo basics', 'date_release': datetime.date(2018, 2, 15)}, {'id': 8, 'name': 'Odoo 11 Development Cookbook', 'date_release': datetime.date(2018, 2, 15)}, {'id': 1, 'name': 'Odoo 12 Development Cookbook', 'date_release': datetime.date(2019, 2, 13)}]

If you want to fetch only a single record, you can use the fetchone() and dictfetchone() methods. These methods work like fetchall() and dictfetchall(), but they only return a single record and you need to call them multiple times if you want to fetch multiple records.