The modal adverbs 其实 and 确实
The modal adverb (语气副词) expresses subjective judgment or assurance toward an action.
The adverbs 其实 
and 确实 indicate the reliability of information that is being stated.
and 确实 indicate the reliability of information that is being stated.They have the following differences in meaning:
其实 emphasizes some fact.
确实 confirms the validity of that fact.
Let’s compare:
Examples
他其实很聪明
He is actually very smart
tā qíshí hěn cōngmíng
他确实很聪明
He is really smart
tā quèshí hěn cōngmíng
其实 and 确实 are placed before a predicate, which is expressed by either a verb or an adjective.
Examples
其实我想回家
Actually, I want to go home
qíshí wǒ xiǎng huí jiā
这次情况确实比较危险
This time the situation is really dangerous
zhè cì qíngkuàng quèshí bǐjiào wéixiǎn
其实你的观点确实没错
Actually your point of view is indeed correct
qíshí nǐ de guāndiǎn quèshí méi cuò
其实 is often used when an assumption is untrue: we thought one thing, but the reality was different.
Examples
我们都以为她去上课，其实去电影院
We thought she went to school, but she actually went to the cinema
wǒmen dōu yǐwéi tā qù shàngkè, qíshí qù diànyǐngyuàn
确实 can be used as an adjective meaning "reliable", "real". It is usually followed by the particle 的 .
.Examples
这是一个确实的高科技突破
This is a real high-tech breakthrough
zhè shì yì ge quèshí de gāokējì túpò
Pay attention
其实 cannot be used as an adjective
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