These two towns are on the western shores of Lake Como and run into each other. There are plenty of boats to Menaggio, Como and other towns in the southern part fo the lake, and a car ferry form cadenabbia to Bellagio (about every 30mins, it takes 10minutes and costs 7 Euros return). Definitely ask for a ferry timetable at one of the terminals - they are not always easy to understand.
Getting to Como takes 1hr 15 by boat or by bus (C10). Bus is cheaper (3Euros - the boat is 8 Euros) but the boat is more relaxing and scenic.
There is a lakefront walk from Cadenabbia to Tremezzo with many cafes and restuarants which face out to the lake. I can recommend Helvetia in tremezzo (south of the Villa carlotta and near the boat terminal and tourist info) - excellent food and service. We got a substanital 3 course meal for two with wine for 50 Euros. There are also an english tea rooms and a cafe for pizza slices and sandwiches in cadenabbia so ideal places for lunch if you are on B&B only.
There are a couple of shops along the lake including an excellent one for Italian wine and fresh pasta and one for jewellery and glass products. There is a small supermarket/grocery store opposite the tourist info in Tremezzo. There is parking along the lake-front along it is very busy.
I can recommend the Grand Hotel Cadenabbia (see separate review) which is good value and offers great views. For a luxury stay try the Grand Hotel Tremezzo with impressive frontage, a spa centre and a swimming pool floating on the lake as well - but the prices are very expensive.
The Villa Carlotta in tremezzo (next to the Grand Hotel Cadenabbia) is very impressive with extensive gardens. It has 70,000m squared of gardens sectioned into different areas and the house which was built at the end of the seventeenth century, is open to the public and is very impressive. Entry costs 8 Euros. There is a small cafe and gift shop there.
There is a tourist train which runs from tremezzo to Menaggio, but check the timetable as it is not very frequent. A return ticket is 8 Euros. It's a 45mins walk to menaggio but in some sections you'll need to walk single-file on the road.
Cadenabbia is the start of the "Greenway" recommended walk which runs south to Colonno for 10.5km along the lake and up into the lower part fo the hills. It's well signed in the main towna on the lake in this area.