A friendly takeover involves one company agreeing to be bought by another, and is often referred to as a "merger" rather than a "takeover." Managers from each firm will typically meet and freely share information about the companies. As you might imagine, in a hostile takeover, the acquisition target is not too thrilled or cooperative.
In a hostile takeover, a would-be acquirer typically sees some strategic value in another company. It may make friendly overtures about a possible merger and be rebuffed. If so, it may then move on to dealing directly with the target's shareholders, by offering to buy their shares for either a certain amount in cash or an exchange of stock. If enough shareholders respond, the acquirer can gain control. To entice shareholders, the offer will certainly be for a price significantly higher than the target's current stock price. Companies whose share prices have slumped are extra-vulnerable to takeovers.