This "In Sha Allah" is an Arabic word, Let's separate it to know the meaning:

1: In ان: Means If 

2: Sha شاء: Means Wills        = If Allah Wills or Allah willing

3: Allah اللہ: Means Allah 

This word is also used in the Quran,

Surah Saffat: Ayat No 102:

فَلَمَّا بَلَغَ مَعَهُ ٱلسَّعْىَ قَالَ يَـٰبُنَىَّ إِنِّىٓ أَرَىٰ فِى ٱلْمَنَامِ أَنِّىٓ أَذْبَحُكَ فَٱنظُرْ مَاذَا تَرَىٰ ۚ قَالَ يَـٰٓأَبَتِ ٱفْعَلْ مَا تُؤْمَرُ ۖ سَتَجِدُنِىٓ إِن شَآءَ ٱللَّهُ مِنَ ٱلصَّـٰبِرِينَ ١٠٢

Translation: Then when the boy reached the age to work with him, Abraham said, “O my dear son! I have seen in a dream that I ˹must˺ sacrifice you. So tell me what you think.” He replied, “O my dear father! Do as you are commanded. Allah willing, you will find me steadfast.

The phrase 'In Sha Allah' is a sunnah of prophet Muhammad PBUH and we should also say this. Saying "In Sha Allah" has many benefits, such as using this phrase to strengthen their connection with Allah. 'In Sha Allah' can correct any work, making our tasks easier and reminding us that we should obey Allah.

So, everything will be fine (In Sha Allah) when you say this!