As you've probably seen in the other comments, pseudocode is not a specific syntax that anyone agrees on. You'll need to figure out what your professor expects. It should be easy to translate into an actual programming language syntax.

Using your problem as an example, I would start with describing the algorithm in plain language:

1. Iterate the list starting from the second item.
2. Compare it to the preceding item.
3. If it is less than the preceding item, return the current list index.
4. Otherwise continue iterating until you reach the end of the list.
5. If you have not found an item to return, return a default value instead.

(note that the answer in the book is slightly different in that at step 3 it stores the index, then the loop condition checks if there is a stored value.)

This can be converted to code many ways. I'll use C# syntax since that's what I'm most comfortable with, but it would be nearly the same in any language that uses C-like syntax:

int FindFirstDescendingItem(List<int> items)
{
    // note: index 1 is the second item in 0-based arrays
    for(int i = 1; i < items.Count; i++)
    {
        if (items[i] < items[i-1])
        {
            return i;
        }
    }

    return 0; // default value, in this case the first item in the list
}

The pseudo-code used in the book is somewhere in between these two. It uses a mix of English words and common programming syntax (such as := for assignment, which was probably borrowed from the programming language Pascal; := for assignment was used to differentiate from = used for testing equality).

How you represent the actions in pseudo-code are largely up to you, but they should be simple steps like what you would put in code. Any complex logic should be broken into separate steps, and if you refer to them multiple times, consider if a loop or a sub-function would make it easier to organize.