Generally speaking, a horizontally oriented color logo in PNG or JPEG format will typically work best on the web. It's not a law, it's a generalization based on aesthetic preference. If you have a logo at all, chances are "real good" you have it in one of these two formats, if not both.
Print is a different story, but it doesn't have to be complicated, and the platform provides a separate upload link for a print-quality logo. To qualify as a "print-quality" logo, the file should meet minimum resolution requirements (typically 300dpi), but the easiest way to ensure that your logo is top-notch print material is to ask your graphics person for a "vector file". This will usually be provided in PDF or EPS format, which, conveniently, are the formats the platform supports.
NOTE: Our marketing team can generally make a web logo work for print, rest assured. :)
Whether for web or print, logo can be uploaded by taking the following steps: