The main method is "trial and error". I wouldn't bother too much about that. Once you are good enough to use a language, either listen, read, write or talk, these come by themselves. And (with the odd, stupid exception) people are more than happy for you to try to learn their language, than to focus on errors.
That said, if you want to look up a word, this link tells it (and much more useful stuff):
And sorry, I forgot: There are the declensions of course, but that is the advanced training ;-)
'I remember when I were a lad we had to walk on the treadmill all day to get the power to run the fridge. ' 'Sheer luxury! We had to walk 10 kilometres to the local nuclear power station and take back a glowing lump of radioactive material to power it. Mind you, it did last for 10,000 years or so.