Go to www.tumblr.com and click on Login, then enter your email account and Tumblr password.
Once Logged in you can create posts. Here are the different ways to do it.
A. Text
A text post consists of plain text. Images, hyperlinks, videos, and some HTML-based widgets can be added. The raw HTML of the post can be edited.
B. Photo
A photo post consists of a single image with accompanied by a brief description. Photos can be uploaded from your PC, or you can use the URL of an image already on the web.
C. Quote
A quote post consists of title text (the quote) and a single line of body text (citing the origin of the quote).
D. Link
A link post consists entirely of a single piece of descriptive text, which is linked to the website or webpage being described.
E. Audio
An audio post consists of a single .mp3 file (be it a music track, podcast etc), which can be played via a Flash music player. Only one audio post is permitted daily.
F. Video
A video post consists of an embedded video, which can be uploaded from your PC, or imported from websites such as YouTube or Vimeo.