Hello Nenes, and welcome to Seven Forums.
If you want all sites to use compatibility view in
Internet Explorer 9, you will need to press
ALT to be able to click on the
Tools Menu bar item instead to. Afterwards it's the same as in IE8 in the tutorial below.
Internet Explorer Compatilbility View - All Websites
If you only want specific sites to use compatibility view, then you will still need to manually click on the compatibility view icon to turn it blue when it appears in the IE9 address bar, or manually add the website to the compatibility view list.
Internet Explorer Compatibility View - Turn On or Off
Hope this helps,
Shawn