die Stufe
step
A single step of a staircase.
Vorsicht, die oberste Stufe der Leiter ist locker.
Careful, the top step of the ladder is loose.

step / level
Loading your saved state.
step
A single step of a staircase.
Vorsicht, die oberste Stufe der Leiter ist locker.
Careful, the top step of the ladder is loose.

The meaning of 'Stufe' (step/level) is usually clear from context: In connection with stairs, it means a step (m01). In relation to a career or development, it means a level (m02). With devices, it describes a setting (m03).
Ich habe in meinem Deutschkurs die nächste Stufe erreicht.
I have reached the next level in my German course.
The word 'Stufe' (step/level) is a common component of compound nouns that refer to a particular level or phase, e.g. 'die Gehaltsstufe' (salary level), 'die Altersstufe' (age group), or 'die Schwierigkeitsstufe' (difficulty level).
Dieses Computerspiel hat verschiedene Schwierigkeitsstufen.
This computer game has different difficulty levels.
The expression 'Stufe für Stufe' means 'step by step' or 'gradually'. It is often used to describe slow but steady progress.
Wir werden das komplexe Problem Stufe für Stufe analysieren.
We will analyze the complex problem step by step.
When talking about device settings, you use the constructions 'auf Stufe X stellen' (to set to level/setting X), 'auf Stufe X schalten' (to switch to level/setting X), or 'auf der X-ten Stufe laufen lassen' (to let it run on the Xth setting).
Kannst du die Heizung bitte auf Stufe drei stellen?
Could you please set the heating to level three?
class
'die Klasse' and 'die Stufe' can both refer to a level or a stage in a system. In school, 'Klasse' often means a group of students or a school year, for example 'die fünfte Klasse' (fifth grade). 'Stufe' more generally means a level or a step in a sequence, for example 'eine Lernstufe' (a learning level), 'Altersstufe' (age group), or 'Schwierigkeitsstufe' (difficulty level). They can be confused because school years can also be seen as levels. 'Klasse' sounds more concrete and connected to school or classification, while 'Stufe' fits better when you want to emphasize a level or a step in development.

Für diesen Kurs brauchst du Deutsch auf einer höheren Stufe.
For this course, you need German at a higher level.
Meine Schwester kommt nach den Ferien in die siebte Klasse.
After the holidays, my sister will be going into seventh grade.