The iMessage system takes regular text messages and then augments them with an instant message system that creates free conversations between iOS users that runs on an Internet connection rather than regular cellular service. This allows for iPhone, iPad, and iPod Touch users to all communicate, and it will really just take the regular system and add features so that you can keep all types of devices in the communication loop, rather than simply other cellular phones. Since iMessages takes a lot of inspiration from these types of messaging services you have options such as deleting your messages and forwarding them to other users.
If you are looking for how to delete messages from iMessage you essentially tie in to the same way that you would delete regular text messages. The iPhone keeps all of your text messages into a chat log that is similar to an ongoing conversation in IM services like AIM. Open up iMessages and then go to the conversation that you are looking to delete a message from. Go to the Edit button in the upper right hand corner, and it will then change the dynamic of the display allowing you to put checks next to each block of text. Go ahead and begin putting the red check marks next to each text messages you want to receive, both to and from you. Then hit the Delete button in the lower right hand corner of the screen, and the button will list the number of text messages you are deleting. Those specific text messages will disappear while the ones you have not selected to delete will remain the same.
The same process is in place if you want to Forward a text message. Hit the Edit button again and you will be able to put the red check marks next to the specific text messages that you want to Forward, which is the same as with deleting the messages. Hit the Forward button in the lower right hand corner and you will open a New Message prompt with the selected message in the text area. You can then choose whom to send it to as a regular text message. You can do this with multiple text messages from the conversation block, but they will be in the same text message and will not forward separately.