I made the mistake of telling my husband that the metro stations signs are in blue. They were in red. Oops. It did take us a while to spot the metro stations.
My 11 year old son understands the transport system in London, and he found it easy to read the Paris metro map too. At first buying the tickets sounds complicated, but once I did it, it became easy.
A day ticket is called Ticket Mobilis and it is much better to use them rather than the single use ticket unless you are planning to go to only one place and staying there for that day. Else the ticket mobiles is like a one day travel card used in London, it allows unlimited travel on the metro. Ticket mobilis comes in Zone 1-2 or Zones 1-5.