Linking Google Analytics and Google Ads accounts together provides a variety of benefits that enable you to:
See ad and site performance data in the Google Ads reports in Analytics
Import Analytics goals and eCommerce transactions into your Google Ads account
Import Analytics metrics like Bounce Rate, Avg. Session Duration, and Pages/Session into your Google Ads account
Get richer data in the Analytics Multi-Channel Funnels reports
You need to ensure that the login you use to access your Google Ads account and Google Analytics account are the same, that you have Admin access in Google Ads, and Edit access in Google Analytics.
In your Google Analytics Admin area, navigate to the property you want to connect to and click on Google Ads Linking (if it is not visible, then click on All Products and choose from there)
If your login has access to Ad accounts, you will see them available here. Select all the accounts you want to connect to, and then click Continue.
In this section, enable all Views you want to connect to Google Ads and then click on Link Accounts.
At the bottom of the next page, click Done.
That's it! You will now be able to see Google Ads campaign, Group, and Keyword metrics in Google Analytics. You don't need to do anything more as far as Analytics is concerned, but you can also enable the Link from the Google Ads platform, which will enable you to pull in Google Analytics data into Google Ad reports.
To do this, go to your Google Ads interface, select the Tools & Setting section, and click on Linked Accounts.
Click on the Details link for Google Analytics (UA).
Here you will see all Google Analytics accounts you have access to with this login and will see which ones you are already connected to. At the far right, you can link or unlink as the case may be, but in the Views column of the Analytics account you just connected to, click on the pencil icon that will appear when you hover over the view.
You can then select Import site metrics into Google Ads and click Save.
The following metrics are now available in Reports and Columns.
You can also find specific instructions from Google's support article "Link a Google Analytics property to Google Ads" on how to link the 2 accounts together.