Let's start with the basics. What is an SVG file and DXF file?
SVG stands for Scalable Vector Graphic. Essentially it's a drawing that you can change the scale of without losing any quality.
DXF stands for Drawing eXchange File. This is an AutoCAD file that is open sourced so multiple programs can open it instead of the AutoCAD only version DWG.
Most likely if you are looking to convert an SVG file to DXF if you want to send an image to a Silhouette CAMEO (basic software edition), CNC cutting machine, laser cutting machines, or even quilting machines!
Using Adobe Illustrator to convert (more details below)
The online converter tool should be pretty obvious on how to do use it. Most of the time you simply open the file you want to convert and upload it into their conversion tool. After a few clicks of a button, you have a file ready to go. Sometimes there is a charge after the first few
Inkscape tutorials are widely available. I have links below based on your preferred learning style. It really boils down to opening your file in the software, making sure the image is broken down into the right settings, and then saving it again as the correct format.