From Wikipedia:

A blog (an abridgment of the term web log) is a website, usually maintained by an individual, with regular entries of commentary, descriptions of events, or other material such as graphics or video. Entries are commonly displayed in reverse chronological order. …

Many blogs provide commentary or news on a particular subject; others function as more personal online diaries. … The ability for readers to leave comments in an interactive format is an important part of many blogs. Most blogs are primarily textual…

Free blog services allow anyone to sign up for an account and keep a blog, updating it with whatever kind of content they choose.

Blogs can be used as websites or added on to a website to provide easily updated content.

Having a blog on a free service means that you never need to worry about maintenance; the staff of the service takes care of all that.

A blog is especially useful for posting time-sensitive information, like the introduction of new products or upcoming events.

If you wish readers to have immediate access to all blog features such as commenting or searching for old entries, your site should simply link to the blog. If your entries are likely to be mostly informational, and not something readers will comment on very often, then embedding them on one of your site pages is the best option.

One drawback of linking to a blog is that it will look different from your site, and this can sometimes confuse readers. A blog can be made to closely match the appearance of your website, but this carries an extra fee of $100, plus $15 per year on WordPress.

One drawback of embedding is that entries drawn from the blog are “cached”, or stored on your own server. This is done to keep from overwhelming the blog server with real-time requests for copies of the most recent entries. This means that new entries or changes to older entries may not show up for as much as an hour.

Which option you choose should depend on what you want to do with your blog.

WordPress and Blogger services at a glance.

The WordPress interface is busier than Blogger because it allows you to control more things about your account. Posting is just as simple, though. First you need to sign in, which you can do at the right of the WordPress homepage. This will cause a gray menu bar to appear at the top of the page, and clicking on “My Dashboard” will take you to the blog controls.

You can also log in by clicking the “Log In” link at the bottom of your blog’s sidebar, which will take you to the dedicated log-in page.

Once you are at your blog administration pages you can click on the “Write” link at the top left of the page.

You can see that the cursor, in that screenshot, is over the “Write” link. Clicking on that takes you to the “Write Post” page.

You write whatever news or update you have into this form. When you’re done you hit the “Publish” button, which you can see the cursor over in the above screenshot. If you want to finish the post later, click on “Save” instead, and it will be saved as a “draft”. The section of your Dashboard page with the red header will have a link to all your drafts so you can easily find and finish them later.

You don’t need to do anything more, but there are more options if you want to organize your posts. On WordPress, you can use categories or tags or both. The boxes for adding these are below the “Post” box.

Categories are more organized, like a file cabinet. You can have categories inside categories, if you wish, like having folders for different years inside your tax returns folder. If you want a new category, you can add it right on the Write Post page, by clicking the “Add New Category” link above the category box.

Tags are more freeform. If I put a post in the category “Produce” I might give it tags like “new this season” and “heirloom seeds”.

Using categories and tags makes it easier for readers to search your blog for particular topics, and for you to find specific old posts.