hi, ive got a oil leak, when l jack it up and crawl under there is oil dripping from the bottom of the oil filter cap and oil all over the square tank which has the nut to empty the oil, (as you can tell my knowledge of engines in not very good) everthing is tight, (oil filter and nut) ive wiped it all away and within a day is covered again! also a separate question, ive just looked in my header tank and its empty! is this correct? if not how do l fill it and what with! any help would be much appreciated, thanks in advance.
it my not be called a header tank, its the cap that you shouldnt undo when the engine is hot! otherwise steam goes everywhere, (as l found out )

the square thing under the car is called an oil pan. The leak is probably caused by loose bolts around the oil pan. it is easy to fix. Just get a ratchet wrench with the right size socket. and tighten up all the bolts that hold the pan on.

l am not sure what you are calling a header tank

You've got two separate but potentially related problems.

The trouble with an oil leak is that it is very hard to locate. The oil leaks while u r driving & goes everywhere from the wind! It is almost certainly NOT a loose oil pan as they do not just come loose by themselves. If u can not locate the source of the leak u should probably take it in. The head gaskets on subaru engines r known weak points, if u drive ur car hard when it is cold that can cause them to fail. Always let ur car warm up slowly before u drive hard. A failed head gasket could also explain the coolant leak. That is what that pressure cap holds in, coolant. You should Absolutely fill ur radiator back up with coolant before u drive it again.

All that said the two problems could also be totally unrelated, but we're talking about 2 key systems in ur engine (lubrication & heat management) l advise u to take ur car to a mechanic right away, especially if u do not have the experience to diagnose the problem yourself. The mechanic should do a compression test to determine the health of ur head gasket, also he should check for coolant in the oil & oil in the coolant.