How Should I Use Tanks

There are a lot of guides on YouTube on how to design tanks and how to make good tank divisions. My question though is how should I use my tanks once I have them on the field. Do I add them to field Marshall orders and use them with the infantry to attack across the entire line? I've also tried putting them in their own armies and using the spearhead command to attack certain point but the tanks end up just spreading across the entire line anyway. (I'm not very good at micro.)