Mueller laid out very clearly that Russians wanted Trump as president, that Trump's children held clandestine meetings with Russians, that a large number of people in Trump's inner circle were indebted to Russia or working for Russian interests (quite a few of whom went to jail for these actions), that there were many reasons why colluding with the Russians would have benefited Donald Trump both personally and in his presidential campaign. He also conclusively proved that Trump both planned and acted to obstruct obstruct his investigation in multiple ways.
However, he did not draw any conclusion regarding Trump colluding with Russia.