When you are configuring a Send Mail script step you get the Options dialog shown below. Each of the blue dropdown buttons can open a calculation dialog in which you can configure the content of that part of the email. For both Subject and Message you can set up a calc that includes a mixture of text and field data. For example, instead of: "Hello Friend, how are you today?" you had: "Hello " & <table::firstName> & ", how are you today?", the message would use the value from the firstName field of the current record. Continue with that methodology for the rest of your content.
You can see in the upper part of the Options a couple of ways to send multiple versions of this to all members in a group. Basically, find the set, then send the message with the correct options chosen.