Man, there are a ton of things like this in English... Well, here in America. We call them Idioms and they were a source of much humor with English students on my trip to Japan. I will just start with some of the ones that start with the letter 'A'.
A fool and his money are soon parted
This idiom means that people who aren't careful with their money spend it quickly.
A little bird told me
If someone doesn't want to say where they got some information from, they can say that a little bird told them.
A OK
If things are A OK, they are absolutely fine.
A1
If something is A1, it is the very best or finest.
About face
If someone changes their mind completely, this is an about face. It can be used when companies, governments, etc, change their position on an issue.
Above board
If things are done above board, they are carried out in a legal and proper manner.
Achilles' heel
A person's weak spot is their Achilles' heel.
Acid test
An acid test is something that proves whether something is good, effective, etc, or not.
Across the board
If something applies to everybody, it applies across the board.
Against the grain
If doing something goes against the grain, you're unwilling to do it because it contradicts what you believe in, but you have no real choice.
Ahead of the pack
If you are ahead of the pack, you have made more progress than your rivals.
Albatross around your neck
An albatross around, or round, your neck is a problem resulting from something you did that stops you from being successful.
All along
If you have known or suspected something all along, then you have felt this from the beginning.
All ears
If someone says they're all ears, they are very interested in hearing about something.
All fingers and thumbs
If you're all fingers and thumbs, you are too excited or clumsy to do something properly that requires manual dexterity. 'All thumbs' is an alternative form of the idiom.
All hat, no cattle
When someone talks big, but cannot back it up, they are all hat, no cattle.
All heart
Someone who is all heart is very kind and generous.
All hell broke loose
When all hell breaks loose, there is chaos, confusion and trouble.
All over the place
If something is completely disorganised or confused, it is all over the place.
All road lead to Rome
This means that there can be many different ways of doing something.
All skin and bone
If a person is very underweight, they are all skin and bone, or bones.
All the tea in China
If someone won't do something for all the tea in China, they won't do it no matter how much money they are offered.
Ambulance chaser
A lawyer who encourages people who have been in accidents or become ill to sue for compensation is an ambulance chaser.
An old flame
An old flame is a person that somebody has had an emotional, usually passionate, relationship with, who is still looked on fondly and with affection.
Ants in your pants
If someone has ants in their pants, they are agitated or excited about something and can't keep still.
Any port in a storm
This means that in an emergency any solution will do, even one that would normally be unacceptable.
Any Tom, Dick or Harry
If something could be done by any Tom, Dick or Harry, it could be done by absolutely anyone.
Apple of your eye
Something or,more often, someone that is very special to you is the 'apple of your' eye.
Arm and a leg
If something costs an arm and a leg, it is very expensive.
Armed to the teeth
If people are armed to the teeth, they have lots of weapons.
As cold as ice
This idiom can be used to describe a person who does not show any emotion.
As cool as a cucumber
If someone is as cool as a cucumber, they don't get worried by anything.
As mad as a hatter
This simile means that someone is crazy or behaves very strangely. In the past many people who made hats went insane because they had a lot of contact with mercury.
As the crow flies
This idiom is used to describe the shortest possible distance between two places.
Asleep at the wheel
If someone is asleep at the wheel, they are not doing their job or taking their responsibilities very carefully.
At death's door
If someone looks as if they are at death's door, they look seriously unwell and might actually be dying.
At each other's throats
If people are at each other's throats, they are fighting, arguing or competing ruthlessly.
At odds
If you are at odds with someone, you cannot agree with them and argue.
At sea
If things are at sea, or all at sea, they are disorganized and chaotic.
At the drop of a hat
If you would do something at the drop of a hat, you'd do it immediately.
At the end of your rope
If you are at the end of your rope, you are at the limit of your patience or endurance.
At your wit's end
If you're at your wit's end, you really don't know what you should do about something, no matter how hard you think about it.
AWOL
AWOL stands for "Absent Without Leave", or "Absent Without Official Leave". Orignially a military term, it is used when someone has gone missing without telling anyone or asking for permission.
Axe to grind
If you have an axe to grind with someone or about something, you have a grievance, a resentment and you want to get revenge or sort it out.