welcome

"Bienvenido" is the standard way to express that someone is received with pleasure. Think of it as opening the doors of your home or your space to someone, signaling that their presence is desired and that they are safe and accepted in that environment. In Spanish, this word must agree in gender and number with the person being addressed (bienvenido/bienvenida/bienvenidos/bienvenidas). It is used both in formal settings, like a business meeting, and casual ones, like greeting a friend arriving at your house. It is often paired with "a" to indicate the location (e.g., "bienvenido a casa").
In conversation
Greeting a friend at the door
¡Hola! Pasa, por favor.
Hi! Come in, please.
¡Gracias por invitarme!
Thanks for inviting me!
¡Bienvenido a mi casa!
Welcome to my home!
Note how 'bienvenido' matches the masculine gender of Luis.
New colleague at the office
Estamos muy felices de tenerte aquí.
We are very happy to have you here.
Muchas gracias, estoy lista para empezar.
Thank you very much, I am ready to start.
Bienvenida al equipo, Sara.
Welcome to the team, Sara.
Here, 'bienvenida' is used because Sara is female.
Examples
Bienvenido.
Welcome.
Bienvenidos a la fiesta de cumpleaños.
Welcome to the birthday party.
Sé siempre bienvenido en nuestro hogar, amigo mío.
Always be welcome in our home, my friend.