about time = finally.
It’s about time they got married. They’ve been living together for five years.
(be) about to = almost, soon
He’s just about to blow out the candles on his birthday cake.
after all = after everything that happened / despite the facts
This was an expensive car, but I decided to buy it after all.
all of a sudden = something happens quickly.
All of a sudden, the boy slipped while riding on his skateboard.
as if = similar; something has a similar quality.
His headache was so bad it felt as if his head was in a vise.
as soon as = after something happens; immediately after
Nguyen started to eat his food as soon as it was served to him.
as well as = and
She’s strong as well as beautiful.
at least = to the smallest degree.
Jim forgot it was his wife’s birthday last week. At least he gave her some flowers the next day.