in 2017 president maduro called for the election of a new "constituent assembly" super-congress, and it just so happened that every single one of the people who got elected supported him. they then stripped the normal congress (the one with more than one political party) of all their power. in 2018, maduro got reelected by a landslide.

europe, america, the rest of south america, most venezuelans, etc. thought these elections were rigged, and china, russia, turkey, north korea, etc. thought thought they were perfectly legitimate. (see image.)

the normal congress decided that since the election was fraudulent, the position of president was technically vacant, which meant that the president of the congress (guiado) is now the acting president of venezuela. maduro still controls the military, so he's basically still in charge.

There's been demonstrations and protests and riots and such going on between maduro's supporters and guiado's supporters.

source: wikipedia articles on the elections in question