January 23 is a historic day in Venezuela, marking the fall of dictator Marcos Pérez Jiménez in 1958 and the return of democracy. This year, on the 61st the anniversary, the president of the National Assembly Juan Guaidó was sworn in as the country's interim president. That set up a constitutional crisis which has yet to be resolved.
Guaidó's swearing in was in accordance with a constitutional provision which addresses what to do in a vacuum of power or the absence of a legitimately elected president. In this case, it applied to Nicolás Maduro's re-election in May 2018, which was widely denounced as fraudulent, and his subsequent swearing in on January 10. The National Assembly determined that Maduro was not properly elected, so it fell to Guaidó to step into his shoes as interim president until free and fair elections can be held.
Confused? Here is a step-by step explainer of how Venezuela got to this point: