First, have two young or regular adult Sims. Make them love each other, so then they will soon have the choice to 'propose' to the other Sim. (it depends if you make the guy Sim propose because the girl will have the last name) Then, select 'propose'. After, it should say in the top right corner ''Congratulations! Your Sims just got engaged!! You can have a public wedding, or something more romantic, a private wedding!'' (its your choice, either you can have public or private wedding)
You'll be married, congratulations!! (or you could have just edited relationships when you created your Sims.)
Chat with our AI personalities
ok you have to use lots and lots and lots of romantic interactions! when the sims relationships are high enough they will have the option to get enaged and then they will have the option to get married.
First get the male/female to be friends then flirt with him/her after you filled the conversation bar you will need to "make out" and "woohoo", if you are at this stage you might press "Try for Baby" to have babies and a wife/romantic friend.
So that is what you have to do, if the male/female accept and let's you have "woohoo" or "try for baby" then you are on the right track.
After you had your "woohoo" you might as well with the male/female click on the "romantic" button and then "engage" if you do not have it then you need to "flirt",
"make out" and "woohoo" more for the male/female to accept your engagement.
And when they are engaged you can either click propose/marriage or buy an arch and make a wedding party with a wedding cake.