Let's break it up:
Internal means "inside", whilst "external means "outside". "Conflict", on the other hand means a problem, a struggle.
Now that we know the definiton of each word, we can solve.
Internal conflict refers to a character's internal struggle.
External conflict refers to a character and external forces. For example, it can be between the character and a group. It can also be person to person.
Brainliest would be much appreciated. Have a wonderful evening.