Hi Oscar,
I completely agree with Mel and Rooster. Mel is right, they're easy once you get the hand of it and Rooster is right that the Eheim site should help you. The filter you have looks virtually idential to an Eheim Pro2 or Pro1 style. Here are my comments in case it adds anything to theirs: (note: the terms input/output are relative to the -pump-)
1) Going after it directly, before finding any instrucs: It sounds like you've probably figured out the putting together, maybe just not the priming with water? It might help to picture normal operation. Be sure any shutoff valves are open. Normally you (one way or another!) give a big suck on the air in the output tube and this pulls tank water into the input tube and over the height of the input crook that goes over your tank wall - thus starting a siphon effect which quickly fills the (not running) filter. Once the entire filter and both tubes are filled this way, the only air remaining to be pushed out is the last bit near where you sucked, the output crook that leads to the spray bar (hooked on later.) Once all this water is in and valves are still open of course, you can plug in the filter and, with a few spurts of noise from the remaining air, it should easily push the water over the remaining little crook and start operation. Note that your sink test may not have worked because the heights are wrong for the siphon effect.
2) Going about getting eheim users guides: Checking the startup instrucs from some models of both the Pro1 and Pro2 model lines may be helpful to you. Getting them can be a bit odd. If you have a choice between wired or wireless connection in your home, choose wired because the pdf files will be a little large and slow to download. I've found that pointing your web browser to www.eheim.com and then clicking on the *germany* part of the map and getting the german site (rather than the north american or others) is one way to go (bear with me.) At the german home page look far right and click on EN for english. Then look far left for "downloads", then click the button for "Manuals." Then choose External filters. You should get to a list of pdf files for groups of filter models. If you are unfamiliar with eheim models, you could choose the "professional 2222..." to start and then maybe the "professional II 2026..." as I think they may be roughly similar to yours. Once you open one, be patient! All the languages are run together and the english part will be buried part-way down in the document.
Oh and here's a link that might take you right there if we are lucky:
http/www.eheim.de/eheim/inhalte/index.js...mp;list=afilter
3) Eheim sells a little suction bulb (looks like a gray racket ball) that you can press onto the output tube over the tank and squeeze a few times to accomplish the priming. It has a little one-way valve that dumps air out a little clear air-tube pigtail so that each squeeze is additive to the vacuum. I bought one of these and its a great addition if your pump doesn't have any built-in priming mechanisms (can't tell if yours does from the picture!)
Good Luck and let me know if I can be of further help,
~~waterdrop~~