I have tried eating quite a few ingredients but none of them has had any effect on me, so I cannot learn any properties of ingredients
what am I doing wrong?

You actually do not have to learn the effects the ingredients have, they will still work so long as you make the right combinations. It is a low skill in alchemy, and a low intelligence that causes potions to fail in creation. A little trick is to use a spell that fortifies your intelligence before you make potions, and drink a potion that does the same.

eating an ingredient doesnt show you the effect. you have to have 15 in alchemy to see the first effect.

Thanks guys!

Actually, when you eat ingredients, one of two things happen: you get a message that the ingredient had no effect or an icon will show up in the bottom right corner. It's just that it's usually so fast that it's gone in the blink of an eye until your alchemy skill improves. You can see that something happened though if you go to your character screen and look at the bar for alchemy showing experience (not explaining it well) but if you hover your mouse over a skill, it shows what progression you've made so far.

The comment about identifying the effects that an ingredient delivers refers to when you hover your mouse over the icon of the ingredient in your inventory AND your alchemy skill is 15 or greater.

So even though your alchemy skill may be below 15, you can still figure out what its first effect is if you're quick enough - sometimes You might find it useful to make a note to yourself until you build up your alchemy skill to 15+ so that you can stock up on beneficial ingredients because eating them does improve your skill over time. And if you want to speed things up, there are trainers out there,

If your character's Intelligence is too low to generate a positive result after you eat an ingredient, I'd suggest grabbing a ton of ingredients, then using a Fortify Intelligence potion (as was mentioned above), and chowing down. That way, you'll get the best effect while the potion is active.

Another thought is to train up Alchemy. As I recall, the friendly alchemist in the Balmora Mage Guild who gives you your first few tasks if you care to join up will be more than happy to teach you the skill, and at a good rate as she slowly gets to like you.

Finally, you can make a ring that's enchanted to improve Alchemy. If you intend to go the wandering alchemy merchant route, that's great, but I've never checked how much enchanters charge for it, as my characters usually start with fairly high Alchemy skill.