I do a little scent work with my GSDs for fun. Her litter was bred as police dogs but she came to me as a pet because she was the runt and didn't have the "confidence" they were looking for. She was a bit of a bored terror as a pup so I decided to start giving her "jobs" and this was one of them. It is actually pretty easy to teach. You just need some flags or something to mark the trail with, some super stinky shoes, a long line if your dog is not off leash trained and LOTS of treats you will want 2 types a very high value and a low value. I usually just use her food for the low value so she doesn't end up sick to her tummy from having too many treats and it makes her feel fulfilled because she is working for a "meal". Then I use some juicy ham or chicken as the high value.
1st find a place with little foot traffic. You will never be able to find a scentless area but one that is relatively unused will work. You just don't want him to be too distracted by too many scents when he is starting to learn.
Put one stinky shoe down next to the flag at the beginning of the trail
Then drop a piece of food and step on it and lightly agitate the ground a bit with your foot on the food. This will put your scent on it.
Do this every step and walk toe to heel all the way to your end point placing a flag every 3-5 steps.
Once you reach the end point place the other stinky shoe and fill it with ham and food.
The jump as far as you can away from the trail and go get your dog who should not have seen any of this transpire. It would probably help to bring another person to help and hold him out of sight while you lay the trail.
Take him to to start flag pick up the stinky shoe and have him sniff it when he doe click and give him a piece of food. Then use another piece of food lure him over to the first piece of food on the trail and drop it. he will likely eat both then begin sniffing around this is where his mind really gets to start to work. He will likely sniff every which direction until he finds the next piece. Let him make mistakes and go off the trail a little side to side because that will teach him that there is no food near the other smells but there is food near this specific trail. If he gets too far off though you can lure him back with another piece of food and drop it on the trail try to stay pretty hands off though so he can feel the success of figuring it out on his own. Soon he will reach the end where the smell is really strong and guess what? There is a REALLY yummy treat there too! This will motivate him to keep trying and want to get to the end in the future because he knows if he persists there is something great at the end!
Go to a different part of the field every time you lay a new trail to ensure your old one doesn't confuse him and as he starts to get better start putting a treat every other steps, then every 3 steps, then every 4 steps and so on until he can just follow the trail.
You can also start turns during this process as well make sure you wait until he is comfortable and confident in a straight line though. I teach turns by placing food all the way around the turn pretty close together at first to help them understand that the trails are starting to change direction and as before put less and less as they become more confident with it.
In the beginning you should lay the trail every time but once he really understands it and the turns you can have other people start laying them too to keep it interesting just make sure to bring some stinky objects.
You can also later on teach him to notify you of "dropped" objects on the trail for added difficulty.
I hope this helps you guys get started! I'm not always the best at explaining so if anything seems confusing or you need a more in depth description on anything just ask.
I also do agility with her and she does lots of things around the house like put clothes in laundry baskets, shut doors, pull laundry baskets, etc... and that has really helped keep her mind happy and me sane. I am currently working with Kavik on learning these things and Zeek will too once he has adjusted to our home more.