How goals and actions fit together
A conversion action is one event you track, like a form submission or a purchase. Google groups actions into standard goals automatically, based on the category you give each action, so every action in the Purchase category sits in the Purchase goal. In Google's words, conversion goals “help you organize your conversion actions so that you can easily optimize toward your advertising objectives.” (Google Ads Help)
Account-default vs campaign-specific goals
Any standard goal can be made an account-default goal. All account-default goals are selected automatically when you create a new campaign, and a campaign set to account-default uses every one of them. A campaign set to campaign-specific uses only the goals you pick for it, which can include a custom goal. Google recommends aligning campaigns to the same account-default goals and, when several goals track stages of one funnel, making only one of them the account default.
Where primary and secondary come in
For an action to steer bidding, two things must be true: it is set as Primary, and the campaign uses the goal that contains it. Secondary actions, and Primary actions in goals the campaign doesn't use, show only in All conversions. The exception is a custom goal: a Secondary action inside one is used for bidding when a campaign uses that goal, and a campaign can bid toward only one custom goal. The full breakdown is in primary vs secondary conversion actions.
Changing goals and the Learning status
Google lists a goal change, when the conversion goals or actions a campaign optimizes to have significantly changed, as one of three reasons a bid strategy shows Learning. It says that status never lasts more than 7 days, and that performance typically takes 1 to 2 conversion cycles to converge on the new goal (About Smart Bidding learning). That's why we make goal changes once and deliberately. More on the learning period, and on why a campaign can be pointed at the wrong goal, in your campaign says it's optimizing for leads.
Common questions
What is the difference between account-default and campaign-specific conversion goals?
Account-default goals apply to every campaign set to use them, and they're selected automatically on new campaigns. Campaign-specific goals are chosen for one campaign and can include a custom goal. You pick between the two in each campaign's Conversion goals setting.
Is a conversion goal the same as a conversion action?
No. A conversion action is a single tracked event. A conversion goal is the category-based group of actions a campaign bids toward. An action only counts for bidding when it's set as Primary and the campaign uses the goal that contains it.
Does changing conversion goals put a Google Ads campaign into learning?
A significant change to the conversion goals or actions a campaign optimizes to can trigger a Learning status, which Google says never lasts more than 7 days. Performance can take 1 to 2 conversion cycles to settle. Changes to budgets, targets, creatives or targeting settings never trigger it.
Why isn't my Primary conversion action counting for bidding?
Usually because no campaign uses the goal that contains it. Google's own example is a Primary action in a Submit lead form goal that no campaign selects: it doesn't influence bidding for any campaign and shows only in All conversions.