跳ぶ are both read as
とぶ, the former meaning "to fly" and the latter meaning "to jump" (generally; don't know if they are interchangeable at all).
The compound-verb suffix
〜込【こ】む means that the action "goes in (to)", "enters", etc.
So the word
とびこむ means "to jump/dive into", both literally and figuratively ("jump into (doing) a mountain of homework", "butt in to someone's business", etc.).
とびこむ is written with the "to fly" version of the kanji:
Why is this? When
跳ぶ means jump and
〜込む means "into", why wasn't
跳 chosen for
とびこむ? This doesn't make sense to me at all.