Ask for Help
Unlike many video or computer games, tabletop games are expected to be social experiences. Creating a character without the help of a more experienced player (or preferably, your GM) is going to be frustrating. Your first option should be to ask the rest of the table for guidance.
If everyone at the table is new, consider asking online (like you are doing now). There are many excellent guides online that talk through the character creation process in more depth.
Failing either of these, you might go to your local game store for D&D organized play and ask someone there.
Carefully Read the Rules
All of the questions listed above can possibly be known by carefully reading the entire PHB. The entire first section of that book deals in character creation: races and classes are not all the choices you face. In particular, you seem to have missed the Backgrounds section which explains personality traits, bonds, and other things.
Compare Your Work To Others'
Look at other people's completed character sheets. You can search for pre-generated characters online and the 5E starter box comes with several. This would explain what goes in each cell or line on the character sheet.
The PHB also includes "Building Bruenor" as an example of creating a 5E character. Each section will mention the choices are involved with creating Bruenor and how they contribute to the character. Even as an experienced player, I found these boxes helpful my first time in 5E.
Do It Wrong
You will almost definitely make mistakes. Take this character into a game with more experienced players and let them correct you. Don't get discouraged. Treat it as a learning experience.
Despite the good points made by other answers, I (as a DM) find that this problem happens due to lack of knowledge from new players. They don't bother reading the PHB (understandably) and thus cannot make informed decisions. I avoid trying to help them make their calls and instead use popular class flowcharts I've found throughout the years.
I've linked my favorite one below. My new players have a lot of fun reading this and also understand the point of the class they are playing based on the suggestions of the flow chart.
We essentially guide the players towards a class they like; and we guide their expectation towards how we want that class to behave.
Obviously, results are not perfect, but players realize during the game that they have made the wrong choice (as opposed to us misinforming them), and that the next time they play they want to try another character, hoping they can play it the way the really intend to (as opposed to complaining about their choice).
Best Answer
There are several options you may pursue as a DM to achieve this goal but keep in mind that homebrewing a mechanic for this might bog down, unbalance or leave wide plot/lore implications in your game that might be exploited.
Magical Effects
Modified Reincarnate
You may use a modified version of the reincarnate spell as a way of explaining how 3 owls turned into an elf. Perhaps an archfey had 3 favoured owls as pets. When tragedy struck one day (maybe when a powerful ogre-magi and its army invaded), the archfey's last act was to reincarnate the owls as a vengeful elf.
Wish
Perhaps a wish spell was the cause of that character's origin. An adventurer might have come across a genie and wished for a companion with the wisdom of 3 owls.
Wild Magic
The effects of wild magic was responsible for bringing back Minsc and Boo about a century after his death in the D&D Comics. It wouldn't be too much of a stretch to believe that wild magic could transform 3 owls into an elf. A wild magic sorcerer might have been responsible as he or she was practicing casting polymorph.
Will of the gods?
Perhaps the gods needed an agent to carry out their will. Just as Zeus in ancient mythology was said to have changed ants into men. Maybe a god in D&D whose high priest had recently become corrupted might have chosen 3 watchful owls to turn into a single elf with qualities that the god cherishes.
Madness
Maybe that character is just mad - full on nuts! In the DMG on pg 258 guidelines for dealing with madness in characters can be found. She could roleplay her madness as a character flaw; as someone who sincerely believes she's 3 owls when really she's just a crazy elf.
As a plot hook, you might decide that her madness comes from a curse, perhaps cast upon her by a shadow-druid when she accidentally started a forest fire as a child.
Have Fun
This has potential to be quite a memorable character. I recommend you do not add in mechanical changes such as giving the character special owl powers, because it might unbalance the game. Focus on the narrative, background and role-play aspects to bring this character to life.