u/Significant-Knee4262

This is first campaign I am dm. My group will be entering Phandelver and I only want to handle chapter 2 stuff. I have seen in videos & forums that some have prepped both 2 & 3. That is overwhelming to me . My question is: if I limit info to just chapter 2 stuff how does my group get info for upcoming chapter 3 stuff. Worried if I give chap 3 info they will not be at proper level to succeed. Sorry for long winded question. Thanks for any advice.