the three red wires all need to be joined together in a terminal box, unless you have the type of ceiling pendant that enables you to make the connections within it - sounds like you haven't. two are the loop, the third goes off to the switch. as the red wires are permanently live they DO NOT connect directly to the brown (live) of the light fitting as your light would be permanently on and you wouldn't be able to switch it off.
similarly the two black wires connect together and to the return (blue) wire in your light fitting. again a piece of terminal block may be required.
the third wire (switch live, which may or may not be indicated by a piece of red tape around it) connects to the live (brown) wire on the light fitting.
you might find that you don't have enough space inside the fitting for all those wires and boxes, in which case you might need to (carefully, so as not to damage the wires) chop out a recess in the ceiling for them to fit into.
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