If you want to target specific countries for your campaign and exclude all others, you can use the geotargeting feature.
Go to advanced settings > geo-target.
By default, all campaigns are set to be active in all countries.
If you want to target a region or specific country, select "Certain countries or geographic regions"
From here, you can select certain countries or geographic regions to include. If there's a checkmark next to the region, it means everyone in that region will be able to enter your campaign.
In this example below, all countries in Asia and Oceania will be able to enter the campaign:
If you only wish to restrict the campaign to a specific country, click on the arrow beside the region you wish to select and choose the country like below:
You can also use the search bar to search for the country right away: