FLAC stands for Free Lossless Audio Codec. As the name suggests, it is an audio file format which always maintains the quality of the original audio data (eg CD tracks). Unlike lossy formats that discard parts of the audio stream to produce smaller files, FLAC compressions don't sacrifice sound quality and can still nearly half the file size. In the past, this codec is usually used to create a backup CD.
However, with the large capacity hard drives and fast Internet connections becoming more common, FLAC is also used for everyday listening and online audio streaming. Despite the advantages of FLAC format, there are some situations in which you want to convert them to another audio codec. For example, on mobile devices size still matters, and you can put nearly twice as many MP3 files as FLAC files on a portable music player.
Also, while FLAC is supported by most of the hardware and software players, in some cases you will have no choice but to use other popular codecs such as MP3 or WMA. To convert .flac files to another format you will need to download and install one music converter available. You can also convert these files online for free on https://convertfaster.com/.
Here's what to look for in an audio converter:
At least, there should be a GUI, and may even drag & drop support. Easy to understand the encoding settings is a definite plus because the audio encoding could be mysterious art if you have to configure everything manually.
It obviously depends on the selected codec and encoding quality, but the raw performance can be a major factor if you need to convert a large collection of .flac to .mp3.
Just one note here – you do not need to buy anything. There are also freeware FLAC file converters that you can use.