As I’ve mentioned in Buses are Better! most visitors to Paris will use the underground Metro and often be delighted by how “easy” it is use. The above ground bus system uses the same ticket system, so if you’ve purchase a <<carnet>> you’re already holding bus tickets. And the Bus system will become easy to use too with help from moi!
Unlike the Metro, you can also pay for your bus ride in cash (euros), but it’s more expensive than using a ticket. Last year (2012) the cash bus fare was 2€. (You’ll be handed a regular ticket to use for that trip.) As of today according to http://www.ratp.fr, the cost of a single ticket is 1,70€ and 10 tickets <<en carnet>> is 13,30€.