Slideshare is a website that allows users to upload and share presentations. Users can create a LinkedIn account to upload, view, comment on, and share presentations publicly or privately in formats like PowerPoint, PDF, and Keynote. To upload a presentation, users log into their account and select files to upload, adding a title, tags, category, description, and privacy settings before publishing. Presentations can then be shared on Slideshare or other sites by copying the share link.