Semonkong is about 120km from Maseru. From Maseru, follow the signs to Roma where you will find the only gas station you will encounter during your oncoming trip. Also, there is a small chinese grocery store to stack up on supplies, since Semonkong itself doesn't have that much to offer. Continue going on the narrow tarmac road from Roma towards Semonkong, until after a T-Junction the tarmac will dissapear. It's a narrow gravel road with a lot of potholes, rocks and other obstacles, with some very steep sections. 4x4 cars is realistically the only way you can get to Semonkong. It's inadvisable for novice drivers to go when it rains heavily since the small bridges may overflood and the gravel road may be very slippery.
The journey takes about 3-4 hours. Theoretically it is possible to do in a powerful saloon car, which will take about 5 hours when weather conditions allow. You might not want to do it overloaded and certainly not with your own car. Note that cellphone reception is limited. Semonkong lodge have a free shuttle every tuesday and friday from Maseru to Semonkong they collect you at tourist information in Maseru. Maluti Treks a tour operator has bus from Durban to Maseru on Tuesdays and Fridays as well as tailor made tours to Lesotho. Visit: 
From the bus station in Maseru you can get the large and more comfortable state bus which leaves twice a day. Alternatively you can get a shared taxi throughout the day. In both cases be prepared to wait for the bus or taxi to fill up before leaving. The taxi will generally take about 3 hours and the bus usually takes about 4 hours.
Semonkong is small enough for it to be possible to get around by foot.
You can also go to the viewpoint by car: When you are about to cross the bridge to Semonkong, turn right and follow the signs to Maletsunyane Falls. Drive for about 9KM on a mysteriously good road until you see a sign pointing to your left (you can see the gorge on your left). Go onto the grass road for a while and you have a beautiful view over the entire gorge and the falls.
Although there are some shops which sell basic footstuffs, there's not much in the way of other shopping!