This video by Abby Elizabeth over on her youtube channel shows you a very simple and clear tutorial on how to make chalkboard labels for glass jars.
If you are buying chalkboard paint I have always found the Rustins brand to be really good. You can pick up chalkboard paint in most good paint shops, I’ve bought it before in Colortrend
I would stear clear of the spray paint version as you will have a lot of wastage. Also versions that tell you they are magnetic and chalkbaord generally don’t do either things very well.
You can also make your own chalkboard paint which is really simple to make, there are plenty of recipes on line.
Here is one that is very similar to one I have used before.
It will dry very quickly so I would recommend doing small quantities. The advantage of making your own paint is you can make it in any colour that you like
I used acrylic paint that I picked up at my local art shop (it doesnt have to be a super expensive one) and tile grout from B&Q
I always use a sponge to paint it on as you want to get as smooth a surface as possible and you defnitely need to do two coats letting it dry thoroughly between each.
Have fun making and if you have any questions just ask.