Everyone can register for a free account on iMechanica and post anything of interest to mechanicians.  Posting a blog entry is like sending an email:

1. Log in
2. Click "Post new blog entry" at the top left corner of iMechanica
3. Write a title
4. Choose a channel in the header of iMechanica.  (This step is important if you are posting an adverstisement of a job or a conference.)
5. Write a body of text
6. Attach a file (if you have one)
7. Click "Submit"

The rest is optional. For example, the following topics might be of interest:

• add tags
• make hyperlinks
• paste a Word file into your blog and make it look nice,
• add images
• add equations
• cite articles in journals
• embed a video

Follow a similar procedure to

• post a new forum topic
• post a new image.

Related posts 

• Most journals permit authors to post self-prepared preprints.  You can also quickly find permission of any particular journal. 
• write a blog entry offline using Windows Live Writer
• what happens after you post a blog entry.