Most international flights will park at a gate with a sky-bridge to the terminal building. At the base of the sky-bridge you will be faced with an escalator and stair taking you to the lower level of the airport. You walk down a corridor which may have a nice garden view to reach the main concourse.
If you did not obtain a visa before coming to Indonesia, keep an eye out for the visa counters, which are located in the main concourse near the arrival gates. Visitors from 36 nations, which includes the USA, EU and GCC countries, can get a visa on arrival. The visa needs to be purchased before going through immigration. You do not need to complete any forms or submit photographs to apply for the visa on arrival. The costs is US$25 for a 30-day visa. Do not get in line at immigration until you have your visa.
Note that the visa fees are in US Dollars. If you try to pay in other currencies, they may choose not to accept them, or they will over-charge you. I've seen them ask 10 Euros (7.09 USD) in place of the US$10 fee. Getting your visa on arrival is a two step process. First, you need to purchase a visa coupon at one counter, then take your coupon and passport to the next counter to have a visa placed in it. You will need one completely blank page in your passport for the visa. Entry and exit stamps will take half of another page.
At the immigration counter, submit your passport with visa and the completed immigration form. Immigration will return the passport with the departure segment of the immigration form inside. Be sure to keep the departure card with your passport, since you will need to submit it when you leave.
Once you've passed through immigration, you can collect your bags and proceed through customs. Give your completed customs form to the customs officer, and you'll be asked to pass your carry-on bags through the scanners.