There is a claiming pattern when, in a row (or a column), a number can only go in cells of the same box. So the number has to be in that box, and it cannot appear in the box's other cells, outside the row. It is removed from their notes.
It is pointing the other way round. With pointing, you start from the box and remove candidates from the row; here, you start from the row and remove candidates from the box. The two techniques make up the family of locked candidates: when a number can only go where a row and a box cross, it can be removed from the other cells.
An example
There are no singles and no pointing patterns in this grid. Row 7 is missing three numbers: the 2, the 5 and the 9. Where can the 9 go?
Column 9 already has a 9, in row 5. The cell of row 7 in that column is ruled out.
The cells in columns 2 and 3 are left. You don't know yet which of them holds the 9, but both are in box 7. So the 9 of row 7 has to be in that box.
Box 7 can only have one 9, and it has to be in row 7. No other cell of the box can hold that number: the 9 is removed from the notes of the cell in row 9, column 1.
In column 1, the 9 had two possible places: rows 2 and 9. With the one in row 9 gone, the one in row 2 is left, and it becomes a hidden single.
Notice that, looking only at box 7, there was no pointing to be seen: the 9 could still go in three cells, which are not in the same row or the same column. It was the row that revealed the pattern. That is why it pays to look both ways.
Rows and columns
In a column, the reasoning is the same: if a number can only go in two or three cells of that column, all in the same box, it is removed from the box's other cells, outside the column. There can be two or three cells, always inside the same box, because that is the box that will be cleared.
How to search
Scan rows and columns, not only boxes.Claiming appears when, in a row, a number can only go in two or three cells, all in the same box.
Start with the rows that have few gaps. With three or four empty cells, it is easier to see whether a number can only go in one of the boxes the row crosses.
Check whether it removes anything. The pattern only lets you remove candidates if the number is still in the notes of other cells of the box, outside the row. If it isn't, the pattern is valid, but there is nothing to remove.
After removing, look for singles in the box where the candidate was removed and in the rows and columns that pass through those cells.
Your turn
Find a claiming pattern and cross out the candidates that should be removed from the box. Tap each cell, choose the number and, at the end, press «Check».