Should I have to click on Synchronize every time I want to sync or I can schedule it?

No, you don’t have to click on Synchronize every time you want to sync.

You only need to automate the synchronization process once.

Please follow the steps mentioned below: 

1. Right click on the SF icon in the Task bar

2. Choose Settings in the pop up list

3. Click on Scheduler tab

4. Specify the interval in minutes in the Synchronization Interval field

5. Save 

The application will Synchronize at the time interval you specified.