On May 10 this year, I would like to travel from Torridon, Scotland to Shiel Bridge, Scotland. Preferrably using public transportation. What are my options?
Use a travel search engine which also includes the public transport you expect to use.
Enter locations, set the date and see what comes up.
If I selected the right locations, there are not a lot of options. Basically just one, I'd say.
The 7:45 bus, schooldays only. The best option takes till 12:10, with bus, train and two more buses. The other options take 4 more hours or more beyond that.
It might be worth to check out getting a ride/taxi to a bus stop with more options.
(Note, I do not know the area, relying on internet information for you.)
Barely any - the Highlands of Scotland aren't served by public transport particularly frequently, and the routes that those public transport services take tend to connect to major destinations fairly directly, rather than going via other less major locations.
Essentially, you'd have to get a bus from Torridon to Inverness, from Inverness to Invergarry, then from Invergarry to Sheil Bridge. This will take about 8 hours, according to Google Maps. The direct drive between the two would take about an hour and a half.
On the plus side, it's not a public holiday, else you'd have reduced services...