In simple words
A transit is where a planet is in the sky now, compared with your birth chart. Here, today's Mercury makes a square (90°) to the spot where your Sun was when you were born.
It is a time of pressure that pushes you to grow, and it lasts a day or two (longer when it is retrograde). Your Today page tells you when it is happening for you.
Love
Words may come out sharper than intended. Soften them.
Avoid arguing by text. Talk in person if it matters.
Listen for what is meant, not only what is said.
Work
Read contracts and emails carefully today.
A plan may need rethinking. That is useful, not a failure.
Avoid rushing decisions.
Mood
Mentally restless. Take breaks from screens.
Overthinking is likely. Move your body.
Write the worry down, then put it away.
About the square
A square sets two planets ninety degrees apart. Their needs pull against each other and ask for action. Squares feel like tension or recurring challenge, and they are also where much of our drive and achievement comes from. Working with a square, rather than against it, often builds a remarkable strength.