agglomerative Hierarchical clustering - interpreting results

I have some data where I want to do some agglomerative hierarchical clustering

I have read this link about clustering, but I am having some problems to interpret my results.

My Data looks like this

12001,0.2,0.32,0.9,....
12002,0.22,0.3,0.5,…

where the first value in each row is an unique ID.

In order to to the clustering I delete the first column

X = csvread('yourfile.csv');
 X(:,1) = []; % delete first column

Aftere this I am doing pdist, linkage and cutoff the cluster. Not sure if I am doing this the right way, but how do I know now which unique ID is in which cluster or how to I even interpret my cluster now?

Any help? Thanks