To determine the probability of selecting the letter 'A' from the letter tiles H, O, N, E, S, T, we first note that none of the tiles is the letter 'A'.
The total number of letter tiles is 6 (H, O, N, E, S, T).
Since there are no 'A' letters among the tiles, the number of ways to select 'A' is 0.
The probability of an event is defined as:
\[ \text{Probability} = \frac{\text{Number of favorable outcomes}}{\text{Total number of outcomes}} \]
In this case:
\[ \text{Probability of selecting 'A'} = \frac{0}{6} = 0 \]
Therefore, the probability of selecting the letter 'A' is 0.