one-sided vs. two-sided hypothesis test (exp?)

#1
My first language isnt English so hopefully you guys understand what Im trying to say by one-sided vs. two-sided?

What I found pretty confusing in my stats class is that we'd often just say

alternative hypothesis H1: variable IS NOT 0
or
alternative hypothesis H1: value of the variable is higher/lower than 0

but we would use the same t-values and all..seemingly?

or are the t-values for a one-sided distribution different than those from a 2-sided distribution?

If I do a one-sided hypothesis test do I just take the t-value of 2,5% instead of that for 5% b/c Im only looking at one side of the distribution?

hope this wasnt tooo confusing ?
 

mp83

TS Contributor
#2
For the one-sided you get the 5% (if you set the signifigance at 5%) and fot the two-sided the 2.5% (so ypu still have the 5% sig)