You meet basso after completing chapter one. He is marked on the map by a bird icon. Outside main chapters, you can talk to him and he will offer you additional jobs. New 3-4 jobs appear after completing each chapter so you should visit him after returning to clock tower.You can have unlimited amount of active missions, so you should accept them all. These missions are simple and often require you to steal one specific item. There are 25 of them in total. To track specific mission press (by default) f1, then click "objectives", choose mission, and press "track" at the bottom. You can also track how many you completed in statistics "overall" tab.