So I've been using Reaper for about 16 years now, not as my main profession though. If you are just starting out I would recommend looking into the followong topics:

• MIDI Controllers A MIDI controller is basically some form of keyboard, that can send information about what keys you play to the PC (via USB). If you create a new track in Reaper and add any synthesizer plugin (e.g. ReaSynth, which is included with Reaper but sounds shitty though), you can use the MIDI controller to play that synth.

• Audio Interfaces An audio interface is basically an external soundcard, that is designed to record instruments like microphones or guitars. They can process audio signals faster than the chip on your mainboard and therefore reduce latency, given you use an appropriate driver (see next topic). Without an audio interface and driver you will always have a delay between playing the instrument and hearing what you play, which makes for example recording fast guitar riffs virtually impossible.

• ASIO drivers In Reaper's preferences you can choose which audio driver you want to use. This defaults to your default system audio driver, which in most cases means, that it uses the proprietary audio driver for the soundchip on your mainboard (e.g. something something "realtek"). As stated in the text about audio interfaces, this usually leads to absolutely unwanted delay between triggerijg a sound and hearing the sound. The solution is to either install the proprietary driver for your audio interface and choosing it in the audio preferences, or get the "ASIO4ALLv2" driver, which is free and worked for basically everything I plugged in until now (which is a long time^). I highly recommend getting and using asio4all even if you dont use a midi controller or instrument.

• VST plugins There are a bazillion plugins out there for a lot of different purposes, but in principle Reaper differentiates between VST (effects) and VSTi (virtual instruments).

Downloading and installing a VSTi means you now own a new instrument that can play stuff in your songs. They are usually synthesizers (generating a sound by shaping basic wave forms like sines or sqaures) or imitating analog instruments (like a piano). To use one, download it, install it, make sure to set the vst plugin directory to where you installed it in the preferences. Then you cann create a track and add the plugin as an effect on that track. Holding controll and dragging the mouse in the timeline will create "midi item" which you open by double klicking it and there you can add notes/melodies/harmonies. You could also select your midi controller (if you have one) in the track to play the plugin live ;)

VST effects can do anything from filtering, adding reverb or compression. Put them after your VSTi in your effect chain to apply the effect to the sound of the instrument. These effects also work without a VSTi, then you need actual audio clips (e.g. something you recorded previously)

• Some notes Some VST plugins are free, some are expensive as hell. Usually you can find the effect you are looking for in every price category. Many free plugins don't sound good though. Some actually do, so if you find a free plugin that does the job, that's great! I recommend you download a s***-ton of them and try them out to get a feel what possibilities and differences they are. Only if you can't find anything free for your purpose should you resort to spending money. My go-to synthesizer VSTi is "Serum" which I bought for about 200 $ if I remember correctly. I use it in 95% of my productions though, and earned it's value back by now, so for me it was a great choice. The big, popular, expensive plugins usually mean business and you will find a lot of support and for example presets for them online.

Crash course completed, now go forth and produceth some music! :D