Hello SteveB and welcome.
Surface plane one side of your board, if it is cupped or bowed plane that face first.
Start the cut with both hands on the infeed side, as soon as the board passes through the guard place your left hand on to the outfeed side applying gentle pressure and use your right hand or more preferably a push stick(the flat type) to push the board through( do not push down) don't be tempted to turn the board end to end, this will result in a see-saw effect, if there are some pits in the centre of it when the edges are already smooth and flat ignore them.
Next make sure your fence is at right angles to your table.
Now place the already flattened face against your fence and plane an edge square to this face.
Set up your thicknesser.
Send your wood through with the already planed side facing down, only take a couple of mill. off, if this does not make the board sufficiently flat try again a mill at the time, when this is done, again ignoring centre pits,turn the board over and remove a mill. from the original side.
Continue, alternating sides, the reason for this is that it release stresses from the board and should prevent bowing later.
Finally using your table saw and a rip blade, place the planed edge on the rip fence and remove any waste from the remaining edge.
If the board, in it's original state is badly twisted or bowed I find that pushing it gently across the blade( only removing a little wood at the time), with a little pressure on the trailing end will often rectify the problem .
I am not a teacher and am sure there are others more qualified than me to explain this more clearly and reading back on what I have written perhaps they should.
Always use provided guards for safety.
Dom
