Here are some handy links to help you get the best from getting about Jakarta.
They will help provide you with maps and more information about things to do and see in the city.
http://www.jakarta-tourism.go.id/conten … map-2015-0
http://www.jakarta-tourism.go.id/conten … event-2016
http://www.jakarta-tourism.go.id/conten … t-map-2015
For the free Bus around the city
http://transjakarta.co.id/peta-rute/pet … ur-gratis/
But the service can be a little slow at times so be warned.
The Transjakarta website whilst in Indonesian is pretty simple to follow. Peta means maps and then you get the full map of the bus routes. There are many routes.
The best ones to see things is Corridor 1 Blok M to Kota.
If you want to go to the zoo then take the TJ bus from Dukuh Atas to Ragunan as that's where the Zoo is at Ragunan and its right next to the bus stop.
Harmoni is the main station to change for different places across the city.
You need a card which costs 40k and then its 3500 to ride the bus. (You can buy them at the Bus Shelters)
If really have to take the bus to and from the Airport then take the Damri bus service. There is a ticketing counter at all the terminals in Jakarta Airport and they go all over the city but it might take a while depending on routes. It could be quicker to either take a Blue Bird or a fixed price Golden Bird from the Airport. To the airport taxis or Uber. Uber is normally cheaper.
If you fancy rattling around the city in the train and it is worth seeing some of the old railway stations then you should visit this site for more information
Just watch your stuff and be wary of some the people around you. But the network is pretty good overall and again its cheap. Around 3,500 rupiah for the first 7km. You buy a card at the station and go from there.