I agree that everything is learning at this age. But the biggest thing to do is talk talk talk! Talk about what you see when you're on a walk, at the park, etc. Ask him what colors things are, and other questions, even if you're answering them yourself.
We did baby signs with our boys, and by 13 months, we conversed pretty well with them. They'd tell us when they heard an airplane, saw a tree or a cat, etc. They're noticing everything at this age, so talk about it! I remember on one rare occasion that I was driving alone, I blurted out, "there's a school bus!" and felt really dumb. But it was a habit of pointing things out that my son was interested in.
Kids that age love "finger plays" like Itsy Bitsy Spider. My friend taught me two more verses, substituting "itsy bitsy" with "great big spider" and "teeny-weeny spider." Then you change your actions and voice accordingly, making them huge and exaggerated for the great big spider, and teeny tiny (with just your finger tips) for teeny-weeny. Oh boy, they just die with how silly and fun those verses are!
Also point out letters when you see them. I never would have thought of it with my first one, but my second son was 1 when his big brother got interested in letters, so he ended up learning them, too. He pointed them out on our moving boxes, etc., and usually called them all B or O. But by the time he was 19 months, he knew half the alphabet! You never know what a kid might be interested in.
My friend gave me a book called, "The Busy Book for Toddlers" or something like that. It has lots of different activities for that age group to do, like drawing in cornmeal on a cookie sheet, "painting" the sidewalk or house or fence with water and a big cheap paintbrush, bowling with a soft ball and empty soda bottles, playing "basketball" with stuffed animals and a laundry basket, etc. At the book's suggestion, I remember once I stripped both my boys and put them in the bath tub (in a diaper for the unpotty-trained one) with a dishpan of warm water and gave them measuring cups and the turkey baster and wire whisks and empty food containers and they played in there for ages! For some reason, it was different enough from a regular bath that it was really fun.
Also, when you're reading a book to him, forget the words on the pages and just talk about the pictures. Ask him to point to certain things, find something red, etc. They LOVE this at that age! One of our favorite books was Ten Little Ladybugs. We'd count and learned lots of different animals and insects. We also love Time for Bed (also lots of different animals).