1. A good computer or laptop. Lots of RAM, a newer processor and lots of storage space is necessary. I also recommend an external hard drive that is used ONLY for your music projects. Recording on your local hard drive can bog down because it's trying to run the computer, run the software AND do your recordings.
2. A good digital audio workstation (DAW). You mention FL Studio, can I assume you're doing hip hop? I know it's popular and easy to use, but frankly, it's not one of the best ones. Consider other DAWs with creative functions. For example, a lot of people talk about Pro Tools, but it is lousy for creating new stuff. I've found Logic or Ableton Live much easier for songwriting.
2. A computer interface. Depending on what you're planning to do, the number of inputs will be important. If you're only recording vocals, it only has to have one audio input. If you're doing live bands, you'll need many more. I recommend at least two inputs, so you can record stereo tracks from a keyboard for example.
3. Monitors (or good headphones). You need to be able to hear what you're doing! And more than just hear it, you need to hear it accurately. BTW, DO NOT use Beats headphones! They are hyped in the low end, and your mixes will NOT come out right. You're better off using something like Sony MDR-7506s. It would also be best to have good studio speakers to listen a way other than headphones.
4. Input sources. This could be keyboards, drum machines, software instruments, sample libraries, guitars, etc. This also includes microphones.
5. Cables. LOTS of cables. You'll need to be able to get stuff into the computer through the interface, out of the interface to speakers or headphones, USB cables, speaker cables, guitar cables, etc.
All of this will depend on what kind of music you want to do, and whether you will use live instruments, software instruments or mics.
That's a lot to think about, but there are places that are good about helping you. I don't recommend Sweetwater - frankly, their retail staff is often pretty clueless. You're better off calling a place like Sweetwater, who is fantastic. If your budget is tight, take a look at Monoprice. They have headphones, monitor speaker, guitars, and they are kings for cables. Their headphones are great and WAY cheaper than anywhere else. (Search for model 8323 - they sound like the Sony headphones above, and cost about $20).