This is a pretty general overview of bearing mounts, hopefully it's somewhat helpful. If you would like some more targeted advice, some clarification on your specific project and CAD experience would definitely help
The context of the overall design is important.
Does it need to be able to slide for tensioning purposes? Then a bearing block set in a channel is probably what you would want to design, or grab a predesigned one off the internet (to purchase later, if needed). Tensioning systems are a pain to manufacture and design, and require a lot of extra parts, so this usually only applies to drive trains.
Otherwise, mounting a bearing is pretty simple, and there are a lot of options. It can be made with sufficiently large aluminum extrusion, machined out of a block of metal, plate, or really sturdy angle brackets. Attachment methods could include bolts, pop-rivets or welds, depending your resources.
The main requirement for placing a bearing is a sturdy place to bore a hole that fits the outer diameter of the bearing (main body, not the flange). If the supporting material is thick enough, and the bearing happens to have a flange, you can add a countersink so that the flange does not protrude from the surface of the mount. Generally, it's also good to have two support points for each shaft, so there will be another bearing or a gearbox that shares the shaft. If there is a flange, it is usually easier to put it on the "outside" of the pair of supports.
In terms of CAD, what are you familiar with, and which modeling program do you use? It's possible to design many parts using just basic sketch tools, and extrude or rotate to add and remove material.