紧张 = nervous
担心 = worry / worry about
we can use this word for two cases:
1) when we have no time.
for example, 他现在很着急，因为他就要迟到了。----he is very 着急 now, because he gonna be late.
2) when we are worrying about something.
for example, 他现在很着急，因为他找不到他儿子了。---he is very 着急 now, because his lost his son.