Viibez it's a pretty ambiguous holiday, the short version of the history dictates that, the pilgrims who came to America (more specifically Plymouth Massachusetts) were incapable of surviving in this new land alone, And the Native Americans provided them with skills and food to last them through the harsh winter.
Because they were religiously inclined, and wanted to show thanks , they made a celebration / feast to honor the help that they received. "...render Thanksgiving to the Almighty God for all His blessings."
It wasn't meant to be held as a yearly celebration but as the colonies expanded others held their own celebrations as well, until eventually on November 1, 1777 the first Thanksgiving Proclamation was made by congress.
The modern relevance is Basically a day to keep your friends and family close, and be grateful for the life you have.