One thing I have to say: They are not the same.
HTML is a mark-up language, meaning it cannot change the page after it renders by itself*.
*Most people use other languages, such as Javascript, with HTML which is otherwise called HTML5, in order to create things like games or intricate menus.
BASIC, or the SmileBASIC dialect in this case, is a programming language, meaning you can dynamically change the content after it renders.
This can be used as a standalone language if you want to make a game, etc. It is also much more versatile and as a result MUCH harder to learn.
BASIC isn't just tags and codes. You will have to learn things such as conditionals, variables, and loops.
Variable:
X = 0
X = X + 5
This will initialize and set a variable X to 0, then increase it by 5 in the next step.
Conditional:
IF X > 10 THEN X = 10
This will set a variable X to 10 IF the variable X is greater than 10.
Loops:
REPEAT
X = X + 5
UNTIL X > 10
Alternate loop that is less useful in THIS CASE:
WHILE X <= 10
X = X + 5
WEND
This will increase a variable X by 5 until it is greater than 10.
To clarify: Both loops will do the same thing, but the REPEAT one is better for the thing you're trying to do.
Also, use PRINT "string" to display information on the screen.
There is a blue help button located in the top right corner of the touchscreen. It has a question mark in it.
Pressing it while the cursor is over a command will show a help section written specifically for that command.
Pressing it while the cursor is on an empty line will show a general reference manual that contains many commands for you to type up and press the help button on.
Good luck!