takeovers-what is it all about

I have been doing a little reading on the takeover by Mr Green of M&S in 2004. Everytime the M&S board has rejected his bids for the company dispite it being over the market share price. I always thought that the share holders can wish to sell the shares to Mr Green and not having the bid being approved by M&S board. Why was this the case? Why did mr green had to have your bid formalised by the board? Why can't he just back all the shares from the open market?

Is what i am thinking of is a "hostile takeover" and not a normal takeover. May any explain what the different is any is? thanks

i mean...can;t this mr green do what Glazer did? buying it from the open market instead of waiting his bid to approve by the board.. thanks