in the body field click on plus and select Opena dvanced editor and you can specify the text plus the variable as well.. if you want html format use isbodyhtml flag in properties and include your html as well in text
eg:
"Hi" + Variablename + "<br>The task to to do today is" + Variable2
here <br> is used for break if bodyishtml is true it would go to newlien..
also if you want to add datatable then use html editor and add the table as datatable cannot be directly added…or there is separate activity html content can use it …all spatic data, variables,datatables etc can be added and output can be sent to send outlook mail activity