Buses are usually not covered :/

You have then to pay for the Bus tickets by your self In some Cities you get a discount for the Touristic Public Transport tickets Here a example for Berlin (There are even cheaper normal non touristic daytickets that i use mostly in foreign Cities )
For example for 7,50€ you can travel one day along the Belgian Coast with the Kusttram :D

In Germany more and more cities refuse to sell tickets from the driver in the Bus they recommend to buy them in advance or online (for example via App)
 

There is really no general answer. Look for a travel planner that is good for that city, region or country (sometimes Google Maps also produces usable results) and check the operator's website for fares and where to buy tickets. There may also be a common tariff system for all public transport in a city or region and a website of the transport authority where you can look up timetables and fares.

In Germany, the DB Navigator app also offers local and regional tickets for many regions in Germany. Similar for the SBB app in Switzerland. But elsewhere the answers can be completely different.

Google is je best vriend-soms. IF you google like ´travel from A to B’you invariably get

rome2rio and another site-check that what they advise, do NOT book via them, but then google the company they mention.

The dayticket for KustTram is 8 € since a year or 3-has to be bought advance. It is valid in the whole of Flanders.

MOST west-EUR countries have extensive national all-transit planners, like 9292.nl. Bahn.de works for nearly all (but not100%) of DE. Some countries also have special lower prices passes for junior=<26.

The rather more demanding trick is next: where/how to buy tickets, as very often this is not possible on the car. F.e.e in CITYtransit about anywhere in east-EUR you have to buy off-bus/tram, mostly in kiosks. But the BUS in Barcelona is now only with app and a Spanish complicated procedure-the metro not.

Newbees generally tend to visit well-worn places anyone knows-again use google ´how to get there´ and it will give details. Older more detailed sites/blogs about/from IR-users often mention dozens of interesting places reachable with the pass itself. Do not stuck yourself only in the capitals!

There are some places where the hotels give out free passes for transport in their local area.  This can include local trains as well as trams and buses.  I’ve been given these in Montreux and Thun, but other places do them as well.

Indeed, this is quite common in Germany, Switzerland and Austria, especially in touristic regions.