You are encouraged to experiment. Try entering similar lines with different numbers. It is clear that + is plus and - is minus. Enter lines that use * for times and % for divide. From using % you will pretty quickly see that numbers such as 2.5 can be the result, and that they can also be used as arguments.
Until you have more experience, you might sometimes be surprised or even disconcerted by what you observe. Take things in small steps. Try examples where you are pretty sure you already know the answer, and do the experiment to confirm your understanding. If a result puzzles you too much, don't spend time on it in these early stages.
3 - 5 _2
The _2, instead of -2, might confuse you. Don't worry, it will be explained in a bit.
Most examples in this book show what you should type, indented by three spaces, and also show the result the system displays. This means that you can read the book in a casual manner, without having to use the system to see results. However, the only way you will really learn is by eventually trying the examples and experimenting with your own. Examples are shown in a fixed-pitch font much as they would appear in the ijx window of your system. A larger font is used in some examples to make it easier for you to read and type the example into the system. This is done where you might mistype something because of being unfamiliar with some of the words, or where a typo could have confusing results.
While experimenting, you frequently want to execute minor variations on sentences you have already tried. There are several shortcuts that make this easier. In the ijx window you can move the cursor to any line in the window and press Enter to recall that line as a new line at the bottom of the window ready for editing. You can recall previous input lines for editing by holding down Shift+Ctrl and pressing the up arrow key until you see the line you want to work with.
The examples in most sections are self-contained, but a later part of a section might depend on steps taken in an earlier part. A few sections depend on steps taken in previous sections, but this should be fairly obvious.