Brazil's presidential election is based on majority voting, so having over 50% of valid votes is necessary to win (even if by a single vote). If no single candidate accomplishes this, there's a second round of elections, where only the two most voted in the first round compete, so whichever of them has the most votes will have the majority.

Legislative elections are held by state, but there is no district system like the U.S. Senators are decided by who has the most votes, no majority required (for example, a senator could be elected with just 15% of the votes if everyone else has fewer votes (like a bunch of canditates getting 10%). The House election is awarded to parties by state, and the most voted candidates for each party get their spots. So let's say there is one million votes and 10 spots on the House for a certain state. You divide the total votes (in this case, one million) by the number of spots (in this case 10), getting the electoral quocient (which would be 100k in this example). So if Party X has 420 thousand votes in this state among their candidates, they've reached enough to have 4 chairs for their congressman, and the 4 most voted candidates of that party will be elected, with the rest being their substitutes (in case they need to vacate the chair for any reason).

Apart the election, the actual government system is VERY similar to the US