It's hard to tell without knowing what your objects and textures are and what their relation to each other happens to be for your specific object. However, I would assume that someone exported an object from blender as an .obj file and selected "export materials" so it generated a .mtl file. This mtl (material) file should be imported when you import your object, but in case it doesn't, I suppose, the person also included the texture as a .png file (unless the .png is just a preview of what the model looks like).
Regardless, your steps should be:
Open a new (empty) project in blender
File > Import > Wavefront(obj) from the top and pick your object file.
The import should have imported the material file as well, so long as it is in the same folder as your.obj (model). To check, press Z in the 3D viewport and select either "Material Preview" or "Rendered" from the pie menu. If the materials did load, you should see them.
With your object selected, choose
File > Export > glTF2.0 from the top. In the export settings (right side of the window that pops up), under Include, check the "Selected objects" box and check under Geometry to make sure Materials are set to Export. Don't forget to name your file and pick an export location. Once this is done, click Export glTF2.0 in the bottom right.
Last step - pray everything worked. I have had success and failures exporting to glTF in the past (exporting to Godot game engine). Sometimes some tweaking needs to be done. Frustrating nights, but a good opportunity to learn the "quirks" of blender exports as well.
If this doesn't work, and you're comfortable sharing your file, you can upload it at this link and then edit your question to post the link they give you - https://blend-exchange.com/. Letting users access your file is a quick way to get answers, but we understand not everyone wants to share their private (or purchased) products.