Ok, let's get right to it. Fortune is a small package which spits out sometimes funny sometimes depressing and at times profound epilouges, and cowsay let's a cow(by default) say it.
Installing for linux distributions is very straightforward, use any package installer and install it. For instance
sudo apt-get install fortune cowsay
sudo yum install fortune cowsay
sudo zypper in fortune cowsay
brew install fortune cowsay
Open up the terminal
Type fortune, and then type cowsay Dude!, and if both manages to make you grin then you are all set.
Fortune packages fetches fortune cookies with some base "category" like science or art. you can load specific category by fortune -a science for instance, and if you like being offended (there are very offensive ones too) do fortune -o. People have been making custom database categories and other cool stuff. I think the best is at the basic resource fortune info.
Now the funpart is when you let the cow give you your fortune as follows
fortune | cowsay
If you are not particularly fond of cows and are super into science you can customize the cowsay character (all cowsay characters) to a milkcan (personal favorite) as follows
fortune -a science | cowsay -f milk
Have fun!