There are various ways to understand the source of customer traffic to your website. Some of the most common ones are enumerated here. Please make sure to add UTM parameters to all sources of traffic that you control. Otherwise, Google Analytics will put them all in the “direct/none” catchall bucket and source attribution will become much harder.
For the Google marketing products, UTM parameters are set by default. You have to actually un-set them so that is not an issue.
To see this at work in Google Ads please go into the account and click on the settings menu on the left. In the dropdown, click on Account Settings and you will see this picture
As you can see auto-tagging(UTM is called that here) is enabled by default. Please keep it this way.
For Facebook, you should set UTM parameters on every ad. How to set them is described in detail in this video.
For Bing, you need to go into Account Settings and turn UTM parameters ON ( in yellow highlights) as shown in the picture below
What about other sources(e.g. affiliates, email, etc.) that you may need to track?