The main difference a beginner will notice
The NIV usually uses smoother contemporary English, while the ESV often keeps more of the structure and phrasing found in the original-language text. That can make the ESV feel precise but sometimes denser.
When the NIV may fit better
The NIV can be a strong first choice if you want a Bible that is readable for long stretches, useful in church and easy to follow in a group. Many readers find the sentence flow easier when they are still learning biblical vocabulary.
When the ESV may fit better
The ESV can appeal to readers who are comfortable with more formal sentence structure or who attend a church that regularly teaches from it. It can also be useful when you want to slow down and examine how a passage is constructed.
Do not confuse difficulty with depth
Harder English is not automatically more faithful, and easier English is not automatically shallow. Translation involves choices. A beginner benefits more from understanding whole passages in context than from choosing a version because it sounds more academic.
Use more than one translation when useful
You do not have to make one translation your permanent identity. Reading a familiar passage in both NIV and ESV can highlight wording choices and prompt better questions. Start with one primary Bible, then compare when a verse or paragraph deserves a closer look.