Advertise online (and possibly offline, too, depending on what you're offering and your budget) in that country.
Assuming you're targeting Google search results, make sure you've designated the correct country in the Google Search Console (formerly Webmaster Tools).
Set the correct language for that country in your HTML code, and ensure your site's pages are written in the appropriate language, preferably by a native speaker to ensure you have the correct syntax, spelling and colloquialisms.
If possible, host the website on a server whose IP address is assigned to that country. If you're only ever going to target that country, you may benefit from a country-specific TLD.
Get listed in country-specific directories. For instance, join in-country industry associations that offer online membership directories.
Pursue link opportunities with legitimate business partners and media outlets in that country. (I'm talking about public relations and relationship-building, not what most people call "link building.") The idea is to eventually earn some editorial links from other sites that are located in that country.
Basically, you want the search engines and your human visitors to recognize that your site is from
that country, about
that country and intended for
people who live in that country.
This will maximize the chances that most of the traffic you get is from that country. If you only want traffic from that country and want to turn away all visitors who come from outside, you'll need to set up your .htaccess file to only accept visitors whose IP addresses indicate they're inside your target country. Be advised, this is not foolproof: someone from outside the country could be using an in-country ISP or a proxy server located in the country and still access your site from "outside." Conversely, someone who's in the country might be using an "outside" ISP or proxy and might not be able to get in.
If you really want to restrict to only "approved" people, make it a members-only site and require visitors to apply for access, where you can ask for (and verify) their address before you let them access your content.
Just depends on how tightly you want to lock it down to only people in that country.