Designing simple wrapper around sqlalchemy

I want to create a simple wrapper around sqlalchemy (python3.6) but I'am stuck at the moment where session and table classes mapped. What should I do now? Should DBManager be implemented to provide interaction with all tables (how to implement that correctly?) or it should return object that will interact with certain table/class? Not sure what approach is correct. Also first time working with ORM. Thank you for your time.

from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker
from sqlalchemy import create_engine, MetaData
from sqlalchemy.orm import create_session, Session

from sqlalchemy.ext.automap import automap_base

class DBManager(metaclass=Singleton):
    def __init__(self, config_path=''):
        self._db_operator = None
        self._db_config = {}
        self._db_tables = {}

        self._error = ''

        if config_path:
            self.load_config(config_path)
            self.connect_to_database()

    def connect_to_database(self):
        self._clean()

        DB_USER = ''
        DB_PASS = ''
        DB_HOST = ''
        DATABASE = ''
        DB_PORT = 3306
        try:
            DB_USER = self._db_config['DB_USER']
            DB_PASS = self._db_config['DB_PASSWORD']
            DB_HOST = self._db_config['DB_HOST']
            DATABASE = self._db_config['DB_NAME']

        except Exception as e:
            pass

        connection_string = 'mysql+pymysql://{}:{}@{}:{}/{}?charset=utf8mb4'.format(DB_USER, DB_PASS, DB_HOST, DB_PORT,
                                                                                 DATABASE)

        engine = create_engine(connection_string, echo=True)
        session = Session(engine)

        Base = automap_base()
        Base.prepare(engine, reflect=True)

        user = Base.classes.users
        article = Base.classes.article

        session.add(user(username='ohyeah'))
        session.commit()