schwer
heavy
Having a high weight; the opposite of light.
Der Koffer ist zu schwer, ich kann ihn nicht alleine tragen.
The suitcase is too heavy; I can't carry it by myself.

heavy / difficult
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heavy
Having a high weight; the opposite of light.
Der Koffer ist zu schwer, ich kann ihn nicht alleine tragen.
The suitcase is too heavy; I can't carry it by myself.

The expression 'jemandem schwerfallen' means that something is difficult for a person. The person experiencing the difficulty is always in the dative.
Es fällt mir schwer, diese Entscheidung zu treffen.
It is difficult for me to make this decision.
Whether 'schwer' means 'high weight' or 'complicated' depends on the noun. If it refers to a physical object, it is about weight. If it refers to a task or topic, it is about difficulty.
Dieser Stein ist sehr schwer.
This stone is very heavy.
To express that an action is difficult, you can use the structure 'schwer zu + infinitive' (difficult to + infinitive).
Diese Frage ist schwer zu beantworten.
This question is difficult to answer.
In the meaning 'serious' or 'severe', 'schwer' is often combined with negative events. Typical examples are 'eine schwere Krankheit' (a serious illness), 'eine schwere Verletzung' (a serious injury), or 'ein schwerer Fehler' (a serious mistake).
Der Radfahrer hatte einen schweren Unfall.
The cyclist had a serious accident.
When 'schwer' describes an emotional burden, it often appears with nouns like 'Herz' (heart), 'Zeit' (time), or 'Entscheidung' (decision). The expression 'mit schwerem Herzen' means that you do something sadly or reluctantly.
Er verabschiedete sich mit schwerem Herzen von seiner Familie.
He said goodbye to his family with a heavy heart.
The reflexive expression 'sich schwertun mit' means 'to have difficulties with'. It is always used with the preposition 'mit' and the dative.
Viele Schüler tun sich mit der neuen Grammatik schwer.
Many students struggle with the new grammar.
In connection with food and drink, 'schwer' means that something is very filling, fatty, or rich and weighs on the stomach.
Nach dem schweren Abendessen fühlte ich mich sehr müde.
After the heavy dinner, I felt very tired.
simple / just
'einfach' and 'schwer' are opposites when talking about tasks, questions, or situations. 'einfach' then means: you can understand or do something easily. 'schwer' means: something requires a lot of effort, knowledge, or time. What can be confusing is that 'schwer' can also describe a high weight. In this pair, however, it is not about weight, but about difficulty. For an exam, instructions, or a problem, you can clearly say: 'einfach' or 'schwer'.

Nach dem Unterricht findet Mehmet die Hausaufgabe noch schwer.
After class, Mehmet still finds the homework difficult.
Die neue App ist einfach zu bedienen.
The new app is easy to use.