I have just installed marketpress ecommerce plugin and simplemarket theme

I have got a message at the top of wp dashboard as follows You must enable Pretty Permalinks to use MarketPress - Enable now » because Iam just beginning and have not much experence in setting up a website or ecommerce website I do not know what to do I have used WPMU videos to setup Marketpress ecommerce and install simplemarket I running it on my computer as localhost can any one help me