t test using diversity index

So, I am trying to perform a t-test using diversity indexes, but the biostat book I am using is a little bit confusing.

the calculated t value = -1.911
calculated v value = 196

then they say something about t0.05(2), 196 = 1.972
They seem to have gotten this value from the critical t value table.

They then say that 0.05 < P < 0.10 and that you do not reject the null hypothesis. This is where I am getting confused. Shouldn't I be finding a p-value? How do they know that this 1.972 means I can reject the null?

Please help. I am doing a scientific presentation using this data as well as publishing a paper (hopefully) and need this answered ASAP!