I am making a log cabin,my question is well, actually 2 ,what does the red center block mean,and can I use a rectangle shape instead of a square for the center,will it come out right?

A rectangle center will give you a rectangle shaped block. :D:D:D

The red center was to represent the warmth of the hearth of the home. Some also used yellow.
However, modern quilts use any colour.
It's your quilt, and you can do what ever you want.
A rectangle won't necessarily make a rectangle block if you leave off the firs log, which is normally another square the same size as the center square. Just add your first log on the long side of the rectangle.

She knows her stuff!!!!

Will the shape be okay though,I think that is what I want,I am using farmers type fabric with vegetables.My sister lives in Florida and our Dad use to sell corn and melons off our porch during the summer, I want to make her something to remind her of Michigan,so a red print for the center,corn melons strawberries blueberries and apples,off whites on the other side,I really want to be able to see the veg.print hence the rectangle.At 9.00 ayard I don't want to cut it up till I know it will work

you could test your rectangle with some lesser expensive scraps. that way you won't waste your good fabric.

you can also make a log cabin with a triangle or a diamond shape.

You could make the center square larger to fit your food fabric and just add a few narrow logs around them. That would keep the pictures more intact.
If not, you can cut your logs any width you want to suit the pattern.
The log cabin is very versitile. Have a look at some in the picture gallery here: http://www.quiltingboard.com/user_page.jsp?upnum=2203
The first one from pollyv9 shows what I am talking about with the larger center.

You can also just make your strips wider. That'll show off the fabric nicely.

The red center block represents the chimney of the log cabin.