After launching the program, the first thing is to choose conversion type: Image to PDF or Text to PDF. In Image to PDF mode, you can convert JPG, PNG, BMP, GIF, TIFF as well as other image types to PDF format. In Text to PDF, you can get a created PDF from plain TXT files.
Click Add File to import your desired pictures or text files. If you have a whole folder for conversion, hit the Add Folder button to load what you want. If the files are successfully imported, you can see the file information listed in the file list like the file name, size, etc.
Also, you can add files from the menu. Click File - > Add File(s) or Add Folder ... to browse and locate what you need.