About AO map

You need to multiply by the Diffuse. An easy way is to use a Composite node.

https://ibb.co/xzHRxQJ

I have wonder about this too and I read somewhere that its not really necessary to use it because its a way to fake Global Illumination and V-Ray renders this for you anyway! You can also use the AO map to create edge dirt for a model too.

Thanks both of you.................

You can put it either on the albedo map / base map / color map (yes folks use 3 terms) on a new layer in photoshop or any 2d tool with the layer mode multiply or darken, and than put the result in the diffuse slot in your material slot.

However, if you render with GI enabled in Vray, there is already an AO option and doesn´t cost much more rendertime. This option is ways more flexible as when you use an AO map when from the render to texture dialog.
But, the AO rendered from render to texture dialog is ways better if you want to use the AO map for real time applications because of the padding you can add, that doesn´t come on the other hand in the GI / AO window (because you dn´t need padding for rendered stills and even not animations).

So decide what you chose in dependence if you need it for offline only, for real time, or for both.

padding for realtime applications:
256 = 2px; 512 = 4px; 1024 = 8px; 2048 = 16px etc etc etc etc.

for rendering stills you can ignore it and use AO option in the GI rollout. Yes you can use here also a VrayDirt node like 3DCargo wrote, but this applies only for if you don´t need a seperated AO map for real time applications.

Thanks a lot !