The title of the level, "How did I get here?", is the most important hint. "Here" refers to the page you are currently on, which was reached via a redirect. Examining the source code of the redirecting page, begin.html, reveals unusually space lines of code. The measuring tape in the image is a hint to look at the sizes of each space in characters:
3, 15, 13, 13, 21, 14, 9, 3, 1, 20, 9, 15, 14, 19
Using A1Z26 will give the answer.
communications.html
The URL and the telephone wire in the image are hints that each number represents a country calling code. The third number, 1, can represent either the United States or Canada, so a Canadian flag is visible within the number to both signify the correct country and act as confirmation. The regions represented by each code are:
298: Faroe Islands
262: Réunion
1: Canada (as mentioned)
239: São Tomé and Príncipe
Next, the title α-2 means that each region must be converted into an ISO 3166-1 alpha-2 code. The codes of each region are:
Faroe Islands: FO
Réunion: RE
Canada: CA
São Tomé and Príncipe: ST
Combining these gives the answer.
forecast.html
The letters and numbers to the left of the chessboard represent each row in FEN notation. The notation represents a position that looks like this:
The book with "CHANGES" on the cover refers to the Chinese divination book I Ching, also known as the Book of Changes. This book contains 64 hexagrams with combinations of complete and incomplete lines. The left and right hexagrams have the Chinese names "zhun" (䷂) and "li" (䷝), which must be entered in the format provided.
zhun/li.html
The image is of a gift, which is occasionally used in riddle games to hint at the file extension .gif. verse.gif has frames containing:
The question mark must be the "missing" item referenced in the title. The people appear in order at the end of the first verse of Billy Joel's We Didn't Start the Fire:
Eisenhower, Vaccine
England's got a new queen
Marciano, Liberace
Santayana goodbye
This means the missing item must be Vaccine.
vaccine.html
Googling the title, "10 holes in a comb", quickly leads to the harmonica. A harmonica with 10 holes is known as a diatonic harmonica, and each of the holes can be either blown or drawn. In this level, +n means to blow the nth hole and -n means to draw the nth hole. The image shows that +1 is C, so the harmonica is in the key of C as opposed to other common harmonica keys such as G. The top line of numbers produces the notes F E E D, and the bottom line produces C A B B A G E. All that is left is to put a slash in the middle.
feed/cabbage.html
The URL "irrational" and the emoji in the title hint that the level is about irrational fears. The objects represented by the emoji in the image each have a named irrational fear:
Blood: haemophobia
Snakes: ophidiophobia
Trains: siderodromophobia
The number 4: tetraphobia
Chickens: alektorophobia
Balloons: globophobia
Vomiting: emetophobia
The answer comes from the first letter of each of these fears.
hostage.html
The title "When are you" is a hint to time zones. Take the time zone of each country shown:
Georgia: UTC+04:00
Nigeria: UTC+01:00
Bangladesh: UTC+06:00
Libya: UTC+02:00
Kazakhstan: UTC+05:00
Madagascar: UTC+03:00
Each of this timezones gives a clear ordering from 1 to 6. Putting the
characters on the flags in this order gives the string
aW1wb3N0dXJl, which decodes from base64 to the answer.
imposture.html
"s" refers to the fact that the stylesheet used
has changed from style.css to styles.css. The
new stylesheet imports the old one, as well as containing five classes,
with eight rules per class. Some of the properties are valid, while the
others are made up. Taking the valid properties as ones and the invalid
properties as zeroes, the answer is spelt out in binary and can be entered
in the folder given.
noguessing/board.html
"board", the image of London and the colours suggest that this level is about Monopoly. (x, y, z) means the xth property of that colour, the yth word of the property and the zth letter of the word. Here are the results:
noguessing/notation.html
K isn't for Kalium, it's for Potassium. In fact, there are eleven elements in the Periodic Table with symbols that don't match their names. Putting them in order of atomic number, the ones at the indices given are:
Potassium (K), Lead (Pb), Antimony (Sb), Silver (Ag), Tin (Sn), Iron (Fe), Copper (Cu)
Use the first letter of the current name of each element.
noguessing/plastic.html