stack them to the height you want . fill with compost and then plant up what you want. I have seen them used to grow potates and as they grow another tyre is placed on top.

I assume you mean tyres minus the wheel rim. If they have the rim then the tyre needs to be levered off one side. It will then need turning out so it forms a cup shape. {a tyre replacement company will be able to do this for you, probably for a small fee}

no need to take the rim off unless you just want to stack them. and make sure there not steel radials as they are harder to cut through.
let the air out and cut through them as the top side wall with a stanley and turn it inside out.
rusty rims are good for some types of plants i,m sure.
check out my recycling blog.
http://www.growsonyou.com/usernut/blog/6905-recycling