We feed our two guinea pigs on things like :
They really like green vegetables, but also they like dry things to
nibble and keep their teeth in trim.
We also give them dry guineapig food we put it in a bowl clipped to the wire of their cage so they dont mess it up.
They have water available - we use a bottle because they make dishes messy by kicking things in them.
We found at first our guinea pigs were scared of lettuce - it is cold and clammy. They thought it was trying to attack them !!
I have seen books say to be careful with giving them lettuce because it gives them indigestion ..
We did not give them too much greens at first. Now they will choose themselves some green food and some dry food.
Our guineapigs have learned to stand up and reach up with their noses for food.
Our two live in a cage in the kitchen made of plywood on short legs otherwise the wood tends to get damp underneath if there is no ventilation.
They can also jump up and down about 20 cm, into our kitchen from the garden where we let them run around.
We put a little fence in our garden so they can not eat the flowers .
They very much like eating chrysanthemum flowers.
They can swim and they sometimes fall in our garden pond. It is only 10 cm deep near the edge so they jump out quickly.