garch - How to calculate the conditional variance of a time series?

I am reading a paper where the term conditional variance is mentioned, but I am not really sure what is meant by this and how this can be calculated:

Fig. 2 shows the conditional variances of the centered returns of the series of prices under study.

As far is know the term conditional variances is used only in GARCH models. So, I assume that in order to calculate these variances one has to use a GARCH Model for the returns. First, one has to calculate the returns $r_t = \ln(p_t) - \ln(p_{t-1})$. Then, the returns should be centered via $\hat{r}_t = r_t-\bar{r}$ (quite unsure if this meant by centered). The last step would be to apply a GARCH model. Is this going into the right direction or am I completely lost here?