In Google Sheets, the T.TEST function is used to perform a Student's t-test, which is a statistical test used to determine if there is a significant difference between the means of two samples.

The function compares two sets of data (range1 and range2) and returns the probability (p-value) associated with the t-test.

The syntax for the T.TEST function is as follows:

T.TEST(range1, range2, tails, type)

range1 and range2 are the ranges of data that you want to compare. They can be single columns or rows, or multiple columns or rows.

tails is an optional parameter that specifies the number of tails for the t-test. It can be either 1 or 2. If omitted, it defaults to 2, which indicates a two-tailed test.

type is an optional parameter that specifies the type of t-test to perform. It can be either 1 or 2, representing paired or independent samples, respectively. If omitted, it defaults to 2 (independent samples).

The T.TEST function returns the probability (p-value) associated with the t-test. The p-value represents the probability of observing a t-value as extreme as the one calculated from the samples, assuming the null hypothesis is true (i.e., there is no significant difference between the means of the two samples).

Typically, if the p-value is below a certain significance level (e.g., 0.05), it is considered statistically significant, indicating a significant difference between the means.

Note that the T.TEST function assumes that the samples are normally distributed and have equal variances unless the type parameter is set to 1 (paired samples), in which case equal variances are not assumed.