Judges are supposed to be non-partisan, but in reality a small number of decisions come down to what basically amounts to personal preference. There are sometimes laws and decisions supporting both sides of the argument and the judge is allowed to pick, as long as they can back it up with prior rulings or laws supporting their decision. Once the judge picks, that sets a precedent for future judges to rule the same way since judges tend to value a stable set of rulings and rarely overturn previous decisions (after all the appeals are settled out, of course) unless something major has changed since then.
So if a particular ruling comes down to personal preference and a judge personally leans conservative, they'll likely rule in a conservative fashion on those small number of cases. If they lean liberal, they'll likely rule in a liberal fashion. You often see this in Supreme Court decisions where the justices are split along political lines, with the conservative justices ruling for the conservative side of the argument and the liberal justices ruling for the liberal side.
That being said, the political stance of most lower judges doesn't matter as they have little impact on case law and few opportunities to make political decisions in their job.