Conditionals
What is meant by the 'first', 'second' and 'third' conditionals?

first conditional
second conditional
third conditional

first conditional
This refers to a grammar structure used to talk about the ‘likely’ result of something happening or not happening. The grammar structure is:
if-clause: 'if' + present tense (eats)
main clause: will or won't
If he takes these antibiotics, he’ll get better quickly. If he doesn’t, he won’t.
Note! Certain other modal verbs (for example, might, but not would), can be used in the main clause.

second conditional
This refers to a grammar structure used to talk about an ‘unreal’ or ‘unlikely’ situation. The grammar structure is:
If-clause: 'if' + past tense (ate)
Main clause: 'would' or 'wouldn't'
If my shares went up 500% I’d sell them instantly. (but it’s unlikely that they will go up 500%)
Note! Could and might can also be used in the main clause.

third conditional
This refers to a grammar structure used to imagine the impossible. It is impossible because something happened in the past and can’t be changed. The grammar structure is:
If-clause: 'if' + past perfect (had eaten)
Main clause: would have + past participle (eaten)
You would have passed your exam if you had studied harder. (but you didn’t study hard and you didn't pass your exam)
Note! Could have and might have can also be used in the main clause
Prepositions
When do I use common prepositions indicating place, time and movement?

in, on, at - place
in, on, at - time
to, into, from, out of - movement

in, on, at - place
In is used to talk about position inside larger areas:
Your new shirt is in the wardrobe.
On is used to talk about something’s position on a line or flat surface:
It’s on the top shelf in the wardrobe.
At is used to talk about a ‘point’ rather than a space, and events where people gather:
Write your phone number at the top of the page.
I met him at the Spice Girls concert.

in, on, at - time
At is used to specify a point in time:
I’ll meet you outside the cinema at 7.15.
In is used to talk about a longer period of time (the morning, the summer, 1972 etc):
During the holiday, I usually read in the morning and go to the beach in the afternoon.
On is used to refer to particular days and dates:
It’s Michael’s birthday on Saturday.
In is used to say how much time will pass before something happens, and to talk about how long something takes:
Hurry up, we’ve got Aerobics class in 20 minutes.
I managed to get to Level 3 of Tomb Raider in about half an hour.
With certain expressions with determiners (this, that, some, all, every) and before next and last, there is no preposition.
How are you feeling this morning? You weren't very well last week, were you?

to, into, from, out of - movement
How far is it from the guesthouse to the beach?
If you climb into that hole you’ll never get out of i