This year on 14th Ellul is my late father’s first Yahrzeit. It falls Motzei Shabbat, Sunday. I understand it is customary to learn Mishnayot. As it is Motzei Shabbat, when should this be done? Also, I understand I should bring refreshments to Shul. Do I need to learn a Masechet, so it will be a Siyum, and if so, do I finish the Masechet after Shacharit before the refreshments, and do I need to fast til then?

There are many different customs for marking a Yahrtzeit. Mishnayot is good, doing a Siyum even better, the more you learn in his merit – the better, and that can be as much as the whole day long. Fasting usually will be from the morning of the Yahrtzeit day. If you want to make a Siyum you can have it after Shacharit just before the refreshments, you can fast or not – as you wish, both are valid customs. Tzedakah is also very important on this day. May Hashem comfort you.