• mv .env.example .env to copy the env example to a real .env;
• Go to .env file and configure your MySQL connection and also set your JWT_SECRET;
• npm install or yarn install to install all needed libraries;
• npx sequelize db:migrate or yarn sequelize db:migrate to set the database with its columns and fields;
• yarn sequelize db:seed:all to setup default needed data on db;
• npm start or yarn start to start the server;
• If you want to undo the database creation: npx sequelize db:migrate:undo or yarn sequelize db:migrate:undo;

Front-end app here: React OLX