Here is a list of the American Standard Code for Information
Interchange (ASCII codes), a characterencoding scheme.
Danish and Norwegian alphabeths contain the vowels
Æ, æ, Ø, ø and Å, å —
They correspond to Ä, ä, Ö, ö and Å, å in Swedish
Á = Á
Â = Â
À = À
Ã = Ã
Ä = Ä
Ç = Ç
É = É
Ê = Ê
È = È
Ð = Ð
Ë = Ë
Í = Í
Î = Î
Ì = Ì
Ï = Ï
Ñ = Ñ
Ó = Ó
Ô = Ô
Ò = Ò
Õ = Õ
Ö = Ö
Þ = Þ
Ú = Ú
Û = Û
Ù = Ù
Ü = Ü
Ý = Ý
Ÿ = Ÿ
Œ = Œ
Æ = Æ
Ø = Ø
Å = Å

á = á
â = â
à = à
ã = ã
ä = ä
ç = ç
é = é
ê = ê
è = è
ð = ð
ë = ë
í = í
î = î
ì = ì
ï = ï
ñ = ñ
ó = ó
ô = ô
ò = ò
õ = õ
ö = ö
ß = ß
þ = þ
ú = ú
û = û
ù = ù
ü = ü
ý = ý
ÿ = ÿ
œ = œ
æ = æ
ø = ø
å = å

The ASCII Code
Most modern characterencoding schemes are based on ASCII, but support many additional characters. The printable ASCII characters represent letters, digits, punctuation marks and some other symbols. The ASCII table has 128 characters. The first 32 codes are "nonprinting characters"  but at 33 "it starts", and there are 95 printable characters. Also, an extended ASCII set contains 256 characters.
Unicode is a major development on top of the ASCII code, and handles alphabets of many nations and symbols. ASCII was incorporated into the Unicode character set in 1991, and the first 128 Unicode characters are the basic ASCII table. Further, the first 256 ASCII characters are in the ISO 88591 character set.
There are other coding systems around as well.
Here is how to handle the basics: Find a good chart and write an ASCII code in your HTML document like this: &#XXX; if the HTML code contains three digits between &# and ;.
If only two digits go into the code, write the two numbers into the &#XX;. If four or five numbers are given, as in some recommended replacement numbers, write &#XXXX; or &#XXXXX;, as the case may be. But check if the most used browsers today can handle what you come up with, as browsers differ in what codes they can handle. You could try Google Chrome, Internet Explorer / Edge, Firefox and Opera, among others, and see if they respond all right to your code. If the biggest browsers do not handle it, there may be little to do about it.
Nearly all of the following ASCII characters here may be used today. However, Nos. 127255 may vary with the implementation system, and numbers 149, 150 and 151 are in a process of being replaced by XXXX numbers (four digits): it could be good to know.
000 is � 001 is 002 is 003 is 004 is 005 is
006 is 007 is 008 is 009 is 010 is
011 is 012 is 013 is
014 is 015 is 016
is 017 is 018 is 019 is 20 is 21 is
22 is 23 is 24 is 25 is 26 is
27 is 28 is 29 is 30 is 31 is 32 is
33 is ! 34 is " 35 is # 36 is $ 37 is %
38 is & 39 is ' 40 is ( 41 is ) 42 is * 43 is
+ 44 is , 45 is  46 is . 47 is / 48 is 0
49 is 1 50 is 2 51 is 3 52 is 4 53 is 5 54 is
6 55 is 7 56 is 8 57 is 9 58 is : 59 is ;
60 is < 61 is = 62 is > 63 is ?

64 is @ 65 is
A 66 is B 67 is C
68 is D 69 is E 70 is F
71 is G 72 is H 73 is I 74 is J 75 is K 76 is
L 77 is M 78 is N 79 is O 80 is P 81 is Q
82 is R 83 is S 84 is T 85 is U 86 is V 87 is
W 88 is X 89 is Y 90 is Z 91 is [ 92 is \
93 is ] 94 is ^ 95 is _ 96 is ` 97 is a 98 is
b 99 is c 100 is d 101 is e 102 is f 103 is
g 104 is h 105 is i 106 is j 107 is k 108 is
l 109 is m 110 is n 111 is o 112 is p 113 is
q 114 is r 115 is s 116 is t 117 is u 118 is
v 119 is w 120 is x 121 is y 122 is z 123 is
{ 124 is  125 is } 126 is ~ 127 is

128 is € 129 is
130 is ‚ 131 is ƒ 132 is „ 133 is … 134 is † 135 is ‡ 136 is ˆ 137 is ‰ 138 is
Š 139 is ‹ 140 is Œ 141 is 142 is Ž 143 is
144 is 145 is ‘ 146 is ’ 147 is “ 148 is
” 8226 is • 8211 is – 8212 is — 152 is ˜ 153 is
™ 154 is š 8250 is › 156 is œ 157 is 158 is
ž 159 is Ÿ 160 is 161 is ¡ 162 is ¢ 163 is
£ 164 is ¤ 165 is ¥ 166 is ¦ 167 is § 168 is
¨ 169 is © 170 is ª 171 is « 172 is ¬ 173 is
174 is ® 175 is ¯ 176 is ° 177 is ± 178 is
² 179 is ³ 180 is ´ 181 is µ 182 is ¶ 183 is
· 184 is ¸ 185 is ¹ 186 is º 187 is » 188 is
¼ 189 is ½ 190 is ¾ 191 is ¿

192 is À 193 is Á 194 is Â 195 is Ã 196 is Ä 197 is Å 198 is Æ 199 is Ç 200 is È 201 is É 202 is Ê 203 is
Ë 204 is Ì 205 is Í 206 is Î 207 is Ï 208 is
Ð 209 is Ñ 210 is Ò 211 is Ó 212 is Ô 213 is
Õ 214 is Ö 215 is × 216 is Ø 217 is Ù 218 is
Ú 219 is Û 220 is Ü 221 is Ý 222 is Þ 223 is
ß 224 is à 225 is á 226 is â 227 is ã 228 is
ä 229 is å 230 is æ 231 is ç 232 is è 233 is
é 234 is ê 235 is ë 236 is ì 237 is í 238 is
î 239 is ï 240 is ð 241 is ñ 242 is ò 243 is
ó 244 is ô 245 is õ 246 is ö 247 is ÷ 248 is
ø 249 is ù 250 is ú 251 is û 252 is ü 253 is
ý 254 is þ 255 is ÿ

Added: 596  an inverted small c followed by a colon  is ɔ: which means "that is to say; namely", and is named
scilicet. It is a typographic sign, but is not used as much as during the centuries before the Internet appeared. Scilicet signs appear for most part in books that are older than the Net.
There is more to go into still, but I hope the above helps as a start.