An uptrend is defined by two things repeating: higher highs (HH) and higher lows (HL). Each rally pushes above the previous peak, and each dip stops above the previous trough. As long as this pattern holds, buyers remain in control.
Why the higher low matters most
The higher low is the more important of the two. It shows that buyers stepped in early, unwilling to let price fall as far as it did last time. When a higher low forms and holds, it often gives the cleanest, lowest-risk entry into a continuing uptrend.
Using it in practice
A common approach is to wait for a pullback into a fresh higher low, look for signs of buyers returning, and place a stop below that swing low. If price makes a lower low instead, the uptrend structure is in question and you should stand aside. Remember that trends end, so no HH/HL sequence lasts forever.
As long as price prints higher highs and higher lows, the path of least resistance is up.