Gravel Riding is one of the most varied types of cycling there is - a gravel bike can be used as everything from a normal road bike, to a cyclocross bike - to a bike which is used to tackle gnarly singletrack. The range of tyres available for your gravel bike will depend a great deal on the type of wheels that you have fitted to it - many gravel bikes use mountain bike wheels, and as such can accommodate a wide range of tyres suited for off road use, whilst some gravel bikes use road bike wheels which lend themselves to a broader range of tyres more suitable for hard surfaces.
The main choices for gravel riders is between semi slick tyres and aggressive tread pattern tyres. Semi slicks are more suited to harder packed surfaces, whilst the aggressive tread pattern tyres, not dissimilar to mountain bikes tyres are better suited to riding looser and even muddier surfaces. There’s also a choice to make in the compound of the tyres that you choose, a harder compound is better suited to asphalt and compact gravel - as it deforms less and wears better - but softer compounds are much better for those straying into harder, off road terrain.