fore,
You cut off scions right before you use them. You can store them in the refrigerator for 2 or 3 weeks. You want to do scion grafts just as the tree is breaking dormancy.
First you cut into the trunk where you want the new branch, then cut the scion. You want the scion to be woody. Tan wood. The shoots we remove when we decandle are still green. Too young. Choose scions that aren't really strong. They would demand too much energy. The medium strength shoots are best.
A tip: the cut into the stock material (trunk or branch receiving the graft) should be pretty deep. Deeper than you would think. That's the reason many grafts don't take, the cut into the stock wasn't deep enough.