What is meaning of different symbols in image?
In general in probabilities the symbol $\sim$ means "follows the distribution ..", for example:

$$X \sim N(3,7)$$

would mean that the random variable $X$ follows a normal distribution with mean 3 and std. dev. 7. In your example the symbol is used to define the notations apparently: the training data follows the distribution of the real data denoted  $p_{data}$ and the generated samples (whatever these are) follow the distribution calculated by the model denoted $p_{model}$. 

The point seems to be about the distinction between the real distribution of the data and the distribution obtained by the model: naturally one wants the latter to represent the former as accurately as possible, that's the job of the estimation algorithm.

An alternative very common notation would be $p(x)$ for the true (i.e. data) distribution and $\hat{p}(x)$ for the estimated (i.e. model) distribution.