Rasuwa Fort is the name of the border-crossing point on the Nepali side, just before the bridge leading to China. But only a few buildings for the Nepali immigration checks are there.
The last village on the Nepali side, Timere/Piding, is actually 2 km before the border. This is where the Nepali immigration offices are, and where travelers passports are stamped for entry or exit. There are also a few guesthouses and small restaurants.
Buses and minivans run between Kathmandu and Rasuwa Fort. The 140km journey takes 8+ hours and costs NPR500. Buses depart until the early afternoon. Private jeeps (USD60 for up to 4 people) are a faster option, and can make this journey in 5+ hours.
Cross the border
Coming from Nepal
The border is open from 8am to 16am (Nepali time). The Nepali immigration office briefly closes for a lunch break around 12pm.
You'll need to get your passport stamped at the Nepali immigration office in Timere/Piding, 2 km before the actual border. Then walk the rest of the (dusty) road to the border point, or take one of the numerous jeeps that will drive you there.
At the border point, get your luggage and passport checked by the Nepali customs, then cross the bridge on foot into China.
Coming from China
The border is open from 10am to 18am (Chinese time).
After the Chinese immigration checks, cross the bridge separating Tibet from Nepal, and get your luggage and passport checked by the Nepali customs just after the bridge. Afterwards, you'll need to walk 2 km to the village (or take one of the numerous jeeps that will drive you there). At the village, you may need to get your passport stamped at the Nepali Immigration offices.
There are a few small restaurants in Timere/Piding, 2 km away from the border point on the Nepali side.
A handful of guest houses in Timere/Piding provide accommodation for the night, for around NRP 600. If you need Wi-Fi, ask before: it may be on-demand only.