Chicago has 2 main airports: O'hare and Midway. Both are about similar distances to downtown, and both also have public transportation to get into the city. O'hare is typically busier since it is a huge airport hub in the US (which tends to bother a lot of people), so fly in through Midway if this is an issue (I personally prefer Midway).
If you want to use the CTA Train to get into the city (very easy and much quicker if there is traffic), use the BLUE Line from O'hare and the ORANGE Line from Midway. Both will lead you straight downtown to the Loop, or to a number of different stops along the way if that is what you need. It costs about $2.25--and you can even load up a pass with more money if you want--and takes about 30-45 minutes to get downtown. A taxi into the city will run you between $30-50, depending on where you are going, and take around 30-45 minutes without traffic (traffic can double or triple that time!).
Cabs are plentiful in this city, especially if you are staying in a popular area. Uber is a way of life here as well (definitely download the app before you come if you don't have it).
The CTA (Chicago Transit Authority) trains and buses are extremely easy to use and a cheap way to get around the city. Fares start at $2.25 and you can get a pass to add more money to it. The train lines, or the "L" as locals call it, go through different parts of the city and they all meet downtown and circle around the Loop. It is actually a really cool way to see the city! Bus routes run through the entire city and are easy to navigate. I recommend using your Google Maps to figure out the best route via public transit if you are interested in trying it out.
If you're a city biker, you are in luck! Chicago has a great bike rental system here (like all major cities these days) called Divvy. A 24-hour pass will cost you $7. It is a great way to ride around and the city, see sites, and ride along the lake. There are designated bike lanes in most areas to keep it safe. Keep your wits about you though because other bikers, drivers, and pedestrians can get a little aggressive at times.
WALK!!! Chicago is such a walkable city. This is my favorite part of exploring different neighborhoods. It is so easy to fall in love with the architecture and beauty of the city just by walking!
