Depth of field - trials and tribulations

I decided to make my blip today with my test photos for an online photography course I'm doing.  I have never quite got depth of field and this is the third course I've done where I have tried to understand it!

I tried a simple (and not very good!) still life set up as these are easy to do at home and tried out two settings, f2.8 and f22 and voila - I appear to have managed to duplicate one of the examples given in the course!
My biggest challenge was trying to manage the exposure as I used a studio light so there were several total disasters, both over and under exposed but I got there in the end.  I still need to do a "proper" image for this module where it demonstrates that I have understood depth of field but that's a challenge for another day.
I'm quite fond of landscapes so I may try and have a go at an image to submit at some point in the next few days...need better light than today though as it's dull and misty today.  Off to see my step-daughter and her hubby for lunch which should be a very pleasant way to spend an afternoon.