Malt extract is concentrated brewers wort. You can get it in liquid form, LME (liquid malt extract). Alternatively, you can buy it in a fine, dry granular form as DME (dry malt extract) or spray malt.
Unlike pale malt which accounts for the majority of grains used in the brewing of English ales, specialist grains need not be mashed. The malting house treats them so the starch has been converted to sugar.
Hops give the bitterness to balance the malt’s sweetness. They are also a preservative. There are numerous types of hops.
Yeast transforms sugars in the wort to C02 and alcohol. Yeast comes in liquid and dry form for the homebrewer’s use. There are multiple liquid yeasts around to suit each type of beer.