XNALara is a 3D posing program for novices, and people who just want to pose their favourite video game characters. It's very old but still works just fine for posing models. The real reason XNALara is important these days, however, is that there are a huge number of 3D models on the internet that can only be found in XNALara formats (mesh and ascii mesh). These models can be easily chucked into XNALara if you want to do some simple posing - but more advanced 3D software like Blender won't accept it.
(by the way, this page focuses on Blender because it's free. Free stuff is good.)
(This only applies to 2.81 blender) Open blender, go to file->import and you should see a new option to import XNALara models. Once you've imported the model of your choice, export as a .obj. Now the model can be used in anything you'd like.
IF YOU HAVE AN ADOBE ACCOUNT, you can use Mixamo to create easy animations with your fresh new .obj model. Upload the file to mixamo, choose your animation, and download it as a .fbx file.
When you import this file into Blender, you'll find it doesn't have any colour. You need to create a new material and change its base colour to 'image texture'. Then select the image texture your XNALara model came with, and go through the model selecting each piece and choosing the material. If your model came with multiple textures, you may have to use trial and error to find the correct one - or there may be different textures for different pieces of the model.
Assuming you now have a funky 3D model doing a tiktok dance in Blender, point a camera object at it and go into the output tab (the one that looks like a printer). Select your output format as a FFmpeg (you could do AVI if you're a weirdo), and the wrapper as an MMPEG-4. Now, go up to the top tab and select render->animation. A new window will open and slowly render each frame in turn. At the end of this you will have a .mp4 file at your chosen output destination.