In the modern musical landscape, technology is everywhere. Setting up a studio or DJ booth takes a certain amount of equipment depending on how you lay it out, and one of the most common pieces of gear you'll need is the audio interface. Whether you're connecting analog sound systems to a digital workstation on your laptop, plugging an instrument into a virtual amp or simply looking for a way to get two stubborn components in touch with one another, an interface is probably what you're after.
Like a lot of other pro audio equipment, interfaces come in plenty of shapes and sizes. For home studios, DJing or semi-portable setups, your best bet will be desktop interfaces like the Universal Audio Apollo Twin DUO or the Focusrite Scarlett 2i4 USB Audio Interface. These don't take up too much space, and they're essentially plug-and-play, making it relatively quick to connect and get started.
If you want something a bit more permanent for a high-end professional studio or a road case rack for a serious touring rig, then you're looking at stepping up to a rack-mounted interface. Since these are designed for demanding professional use, they tend to support more audio sources plugged in at once and usually have other small perks over the desktop models. For instance, one thing you may find in a rackmount interface but not in a smaller unit is an expansion slot. The Universal Audio Apollo Duo is an example of that, available with an optional Thunderbolt expansion card for better Mac connectivity.
Maybe what you're after is something that you can grab and go: something that's the perfect partner with a laptop or tablet. In that case, there are all kinds of portable options to choose from, such as the Apogee Duet, Apogee ONE or IK Multmedia's line of iRig interfaces. When you want an interface you can take anywhere and set up in seconds, you'll be happy to know that those kinds of devices are well-represented in this selection.
No one knows your audio setup better than you, so choosing the right audio interfaces to use with it is definitely a personal thing. Think about the features you need and want for your personal tastes, and you won't have trouble picking out a great audio interface that delivers amazing results.