By setting up goal tracking, you are telling Google Analytics what information to prominently display in your Google Analytics account:
"Having properly configured goals allows Analytics to provide you with critical information, such as the number of conversions and the conversion rate for your site or app. Without this information, it's almost impossible to evaluate the effectiveness of your online business and marketing campaigns [such as Adwords]"
By having Goal Tracking and Google Adwords activated, rather than viewing conversion rates for your website as a whole, you'll be able to view the direct conversion results of each Adword Campaign.
Read more about Goal Tracking here: https://support.google.com/analytics/answer/1012040?hl=en
How To Set Up Goal Tracking:
1. Open Google Analytics for your website
2. Open the "Admin" options (you can find this at the bottom of the Right-hand side menu)
3. Open "Goals", this should now be an option on the far right of your screen.
4. Add a "New Goal"
5. Choose Custom
6. Name your Goal I.E. "Checkout Complete"
7. Choose Type: Event
8. In Goal Details set:
1. Category to "Checkout"
2. Action to "Complete"
3. Other fields can be left blank
9. (Optional) Turn on: "Use the Event value as the Goal Value for the conversion", this will show the monetary value of your conversions.
This should look like the below, can now be saved.
Conversion results can take between 24-48 hours to show in your Analytics reports, this is the time Google's own systems need to process the analytical data.
To read more about basic Google Analytics set up and cross-domain tracking, read our guide here: https://tonic.uservoice.com/knowledgebase/articles/1139806-google-analytics