"Was wondering what the best way to clean it and stain it"
Oak is an "odd" wood choice ( imho ), nevertheless, let's play with the toys available...
First, the best way to start is to dismount the wood. In this case it looks like you have to remove only three items, so the task should be manageable.
Clean up the wood, via sanding. You might consider rounding or fairing those edges a bit, though anything beyond "getting down to bare wood" should be considered decorative, rather than required. Sand, using moderately coarse ( 100 grit or so ) down through finer and finer grades till about 320 grit. BE SURE TO CLEAN FULLY between grades, by using a vacuum and/or tack cloth. You must remove all residual grit from the coarser grade prior to using a finer grade ( else you get scratches ).
Now you are ready ( after a final vac/wipe down ) for finishing. I personally dislike any stains, and usually avoid them, preferring to let the wood age naturally, but may others like to stain. Any standard stain will do. Apply as directed by the label.
After the stain process is complete, then here is what I would recommend ( I'm donning my Nomex flame resistant suit as I type! ):
Apply one coat of clear epoxy resin ( NOT vinyl ester ). This will act as a barrier coat, making the wood "water resistant". Let the epoxy cure till hard. If in doubt, wait another day...
Wipe the hardened epoxy with acetone ( to de-wax/clean ) and sand lightly with 320 grit to slightly roughen up the finish. Do not sand through!
Now apply your favorite marine grade varnish w/ UV inhibitors. ( epoxy is not resistant to UV )
Let cure/dry till finish is -completely hardened- then re-install.
This will provide you with a good looking piece of wood, that is resistant to splashing and resistant to sun exposure. When the topcoat fails ( it likely will, eventually ) you can lightly sand the topcoat, without removing the epoxy layer and re-finish w/ shellac/varnish.
-edit-
Yes, it could be sun-bleached mahogany. All of my above comments stand, regardless.