The algorithm toolbox offers access to all of Mantid’s algorithms. If you are familiar with MantidPlot it functions similarly. The algorithms are listed in categories and there is also a search bar.
The execute button will bring up the execution dialog for the selected algorithm.
From this window you can enter your input workspace, the parameters for your selected algorithm and your target output workspace.
The algorithms are sorted into categories to make navigating easier. A list of categories that may help you find what you’re looking for can found at Algorithms. To ensure the algorithms are found in sensible places they can be in more than one category.