[wannabesmallholder]

I have bought one of these instead of a heat lamp for my brooder box
https://brinsea.co.uk//bird-breeding-products/brooders/ecoglow-20-chick-brooder/

Do I put the food and water underneath it or to the side?

[Womble]

No, set the height of the brooder to roughly the level of the chicks' backs (you'll have to adjust it as they grow), then put the food and water beside it. The chicks will come out to eat and drink, and will then pop back under 'mum' to warm up again.

Keep an eye on them for the first few days to make sure none of them get caught out in the cold (they'll soon tell you if that happens!), and to make sure that they have all figured out the eating and drinking thing too.

[Marches Farmer]

If the chicks settle down around the edge of the brooder it's too low.  I used to set mine around 15cm high for newly hatched large fowl chicks.