I'm not your country, so I'll also tell you the web address.

1. Naver map (Korean: 네이버지도)
2. https://maps.naver.com

:This is the most used map app among Koreans. I recommend Naver Map because Google Map performance is not very good in Korea.

You can also see the subway app.

Other option is Kakao map.

1. Delivery apps (Korean : 배달의민족, 쿠팡이츠, 요기요)

The good thing about this service is that unless you're really in the mountains of Seoul, delivery is very good. It'll even be delivered to your hotel lobby.

If the food you want isn't available at a nearby restaurant, delivery is also a good option.

1. 음식점 예약 -Naver, catchtable
   (Korean: 네이버, 캐치테이블)

Since these are Korean apps, you have to use Korean, but most of the time, if you search for food names, results will come up.

Since there are often waiting lines at popular restaurants, you can make reservations or there may be a system that allows you to put yourself on the waiting list.

Hope that helps!