Telling me what lesson I have tomorrow and emailing me the results
I would change the data organization to be the opposite way, to have a dict mapping to the two week types containing a dict with a mapping from the weekday to the lessons:

timetable = {"A": {"Monday": ["English", "Maths", ...],
                   "Tuesday": ["Maths", "Computing", ...],
                   ...},
             "B": {"Monday": ["History", ...],
                   ...}}


By the way, it is spelled Biology, not Bioligy.

Then you can just use it like this:

import smtplib
import datetime

TIMETABLE = {"A": [["English", "Maths", ...],
                   ["Maths", "Computing", ...],
                   ...],
             "B": [["History", ...],
                   ...]}

SEMESTER_START = datetime.datetime(2016, 9, 1)


def calculate_week_type(date, start_date):
    """Even weeks since start_date are "A" weeks, uneven are "B" weeks"""
    return "A" if ((date-start_date).days / 7) % 2 == 0 else "B"

def lessons(timetable, start_date, date):
    week_type = calculate_week_type(date, start_date)
    return timetable[week_type][date.weekday()]

def mail_lessons(lessons, to_email='*email*'):
    content = "You have {} today.".format(", ".join(lessons))
    mail = smtplib.SMTP('smtp.gmail.com', 587)
    mail.ehlo()
    mail.starttls()
    mail.login('*email*', '*password*')
    mail.sendmail('*email*', to_email, content)
    mail.close()

if __name__ == '__main__':
    today = datetime.datetime.today()
    mail_lessons(lessons(TIMETABLE, SEMESTER_START, today))


I put the different responsibilities into separate functions, got rid of most of the global variables, and fixed some small differences to PEP8, python's official style-guide. I used a format string, because it is in general faster than string addition (it is usually more readable as well).

I also made the mapping now using numerical weekdays as indices into the internal list of lists, because this is what datetime returns. This way there is no need to translate between the two.