In short, Evo Morales is a socialist politician who acted as President of Bolivia from 2006 to 2019. He was pretty successful, overseeing quite consistent economic growth at the same time as a reduction in income inequality. He's also the first ruler of Bolivia to come from the indigenous population since the pre-colonial era.
In 2009, he introduced a new constitution (following a successful referendum on it), which you can read
here (in English). It includes limiting Presidential runs to 2 consecutive terms.
Then, in 2016, he ran another referendum, aiming to amend the constitution to allow further runs. This referendum returned a "no", 51.3% to 48.7%. However, he instead turned to the Plurinational Constitutional Court and requested that they amend the constitution to abolish term limits instead (for background, the members of the PCC are popularly elected in Bolivia, and it's the highest court in the nation). The court abolished term limits, on the basis that refusing to allow someone to run in the election is a breach of the American Convention on Human Rights.
That brings us to 2019, when Morales ran again for a third consecutive term, and won 47% - 36% (36% being the closest runner-up, a Centrist party). The OAS claimed there were irregularities in the vote count. Cue a coup d'etat by sections of the Bolivian police & military (and supported by the US), and the installation of Jeanine Anez (from a small right-wing party, notably not from the winning party
or the runners up) as President. Anez oversaw a violent crackdown on protestors and journalists in Brazil.
It subsequently turned out that the OAS audit of the vote (that had concluded there were irregularities) was seriously flawed. Then finally in 2020 Anez allowed an election to take place, the result was an overwhelming victory for MAS (Morales' party). Morales will be returning to Bolivia, but won't be taking over as President again.