hiya. welcome to the site! the best setup is sand on the bottom as the substrate (they have a tendency to eat gravel). you could also have large river stones but i dont find they look that good or keep the dirt as well as sand. they like lots of places to hide so you can cut an ice cream tub in half and put some sand on top of it to keep it down. youll also need a good filter as axies are quite messy. heres something i wrote for someone else about cycling. tell me if you dont understand anything:
Ammonia is given off by the axolotl as they excrete. With an established filter (one that has lots of good bacteria on it and has been in the tank a while, adding filter starting products can help) the very harmful ammonia is converted into nitrItes which are a little less harmful than ammonia. With the combination of the established filter, these are converted into almost harmless nitrates which can get harmful if they get too high. This can be helped by removing 10% of the tank water every week or 20% every other week and adding lots of live plants which use nitrates as a fertiliser. You can buy test kits to measure the levels of these substances. A cycled tank should have 0ppm for both ammonia and nitrite and preferably 0 for nitrate too but is allowed to go relatively high. The instructions in the kit should tell you more.
although live plants have their benifits, they do disintergrate and are rather nasty when they do and as they decompose, it can increase the nitrites etc. if you are going to go for live plants, i find peace lilys are great with axies and dont readily disintergrate. if you need any more info just ask