Trans fluid question

How exactly do I know if/when I should add transmission fluid? The dipstick just has two lines, so I assume as long as the red falls somewhere between
the lines it's alright. Am I right on this? I don't want to overfill it.
Second question: What kind of trans fluid should I use? I noticed some of them have different substances, but which ones are okay to use in a 300CE? I don't have a service manual to ask. Thanks!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file
Upload is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.