To compare two things with a short word (one beat, like tall, fast, old, cheap), add -er and use than.
Short words: add -er than
Amina is taller than Lars.
The metro is faster than the bus.
This jacket is cheaper than that one.
Two spelling changes to watch: words like big and hot double the last letter (big → bigger, hot → hotter), and words already ending in -e just add -r (large → larger, nice → nicer).
So it is bigger (not "biger") and larger (not "largeer").
Try it: The metro is ___ the bus. (faster than / more fast than / faster that) Answer: faster than — Fast is a short word, so add -er: faster. Short words do not take "more" (not "more fast"). And the compare word is than, not "that": faster than the bus.
Try it: July is ___ June this year. (hotter than / hoter than / more hot than) Answer: hotter than — Hot doubles its last letter before -er: hotter (not "hoter"). Hot is a short word, so it takes the ending, not "more hot".
Try it: This room is ___ the kitchen. (larger than / largeer than / more large than) Answer: larger than — Large already ends in a silent -e, so just add -r: larger (not "largeer"). Large is a short word, so it takes the ending, not "more large".
Long words: more ... than
With a longer word (two or more beats, like fa-mous, mo-dern, ex-pen-sive), do not add -er. Put more in front, and keep than.
Senfarren View Hotel is more expensive than the hostel.
This book is more interesting than the film.
Physics is more difficult than math for me.
Watch out: most two-beat words use more too: more famous, more modern, more careful (not "famouser"). Words ending in -y take the ending instead: busier, happier.
Try it: This book is ___ the film. (more interesting than / interestinger than / more interesting that) Answer: more interesting than — Interesting is a long word, so use more in front, not an -er ending (not "interestinger"). Keep than for the comparison: more interesting than the film.
Words ending in -y
It is the -y ending that matters here, not the length. Look at the pattern: heavy → heavier · easy → easier · happy → happier · busy → busier. The y becomes ier.
This box is heavier than that one.
Mondays are busier than Fridays.
She is happier than before.
Try it: This box is ___ that one. (heavier than / more heavy than / heavyer than) Answer: heavier than — Heavy ends in -y, so the y changes to ier: heavier (not "heavyer", and not "more heavy" because this short -y word still takes the ending).
good, bad, far
A few common words do not follow the pattern. You just learn these three: good → better, bad → worse, far → farther (or further, which works for any kind of distance).
This cafe is better than the old one.
The traffic today is worse than yesterday.
The station is farther than (or further than) the park.
Try it: This cafe is ___ the old one. (better than / gooder than / more good than) Answer: better than — Good does not add -er and does not take more. It has its own form: better than. ("Gooder" and "more good" are the regular patterns, but good is one of the three to memorize.)
Try it: Senfarren View Hotel is ___ the hostel, and the walk there is ___ I thought. (more expensive than … longer than / expensiver than … more long than / more expensive than … more long than) Answer: more expensive than … longer than — Expensive is long → more expensive. Long is short → longer (add -er). The length of the word decides which one: more for long words, -er for short words.