You can make it into a roll in wax paper and chill or just put it into a container and spoon or cut out when needed.
The idea behind these butters is to bring out the best in whatever you are putting it on. If you have an oily fish like salmon, you want a tart butter so it isn't too rich. To make the butter tart you can use any citrus, wine or vinegar. A good combination for salmon is dill, shallots, wine or lemon. A good combination for steak is tarragon, red wine, shallots and black pepper. Swordfish might like garlic, basil and chipotle.