In my own genealogical research experience (for over 15 years!) The most important thing is to find the birth certificates of your grandparents. If you know their dates and place of birth and / or dates of death, you can start building your tree on FamilySearch and / or Geni.com.
Ancestry and My heritage are paid sites for obtaining documents or contacting contributors.
The 1st site is free. It is owned by Mormons, who digitized most church records, both Catholic / Protestant, and Jewish.
By simply entering the complete civil status of the ancestors, their search engine offers you documents that are immediately searchable, if the microfilms have been translated. If they haven't already been, you will need to search the microfilm of the place of birth for each parent. It is often tedious but it allows you to advance in your research.
You can also create the same tree on Geni.com, which is also largely free.
If you do not have access to paid documents, other contributors to the site will be able to grow your tree for free. I found several cousins still alive thanks to these two sites.
If you need more explanation, you can write to me in private.
Good luck
Elisabeth Stamminger