# When we run many chains at once in an MCMC model, how are they combined together for the posterior draws?

In R, there are packages and functions for MCMC's such as jags.model that allows us to control the number of chains we would like to run, i.e., within jags.model, we can set n.chains = 4 for $4$ chains. The resulting traceplot is multi-color as it traces out the posterior estimates for four separate chains. My question is, when we retrieve posterior draws or estimates from the object, which of the $4$ chains was used? Was it an average? Thanks.