Actually most Mandarin speakers are able to understand simplified Chinese and traditional Chinese, as they have the same pronunciation. However, it is not easy for a Chinese learner to learn both scripts at the same time. For Chinese beginners, it's better to decide which script is right for you. Understanding the differences between simplified Chinese and traditional Chinese will help you make a decision.

Where to Use Simplified Chinese and Traditional Chinese

Simplified Chinese in Mainland China, Singapore, Malaysia

Simplified Chinese is the official script in mainland China, Chinese District of Singapore, Chinese District of Malaysia, and the United Nations. Before you decide to learn simplified Chinese or traditional Chinese, you have to choose what area you will stay in or whose people you will get in touch with. Obviously, more people are using simplified Chinese in the world.

Traditional Chinese in Hong Kong, Macau, Taiwan

Traditional Chinese is widely used in Hong Kong, Macau, Taiwan for some historical reasons. Actually the traditional Chinese was the orginal standard character in China before 1956. To promote Chinese character and eliminate illiteracy, simplified the traditional Chinese became one of the main government works in 1956.

Different Strokes

The main differnce between simplified Chinese and traditional Chinese is that a character in traditional style has more strokes than that in simplified style. That is to say, traditonal Chinese looks more complicated than simlified Chinese. For instance:

English Simplified Chinese Traditional Chinese Pīnyīn
car chē
see jiàn
blue lán

Different Pronunciation

In Hong Kong and Macau, cantonese is the main language. Even though cantonese and mandarin both belong to Chinese branch of the Sino-Tibetan languages, they have different pronunciation almost on every character. For example:

English Simplified Chinese Pronunciation Traditional Chinese Pronunciation
happy 开心 gāo xìng 開心 hoi sam
relationship 关系 guān xì 關係 gwaan hai
China 中国 zhōng guó 中國 zung gwok
Chinese character 汉字 hàn zì 漢字 hon zi
time 时间 shí jiān 時間 si gaan

Different Vocabulary

People who live in mainland China, Hong Kong, Macau and Taiwan have different vocabulary towards a few words. Sometimes it may lead to a misunderstanding or a joke if you are not aware of the difference. For instance:

English Simplified Chinese Pronunciation Traditional Chinese Pronunciation
strawberry 草莓 cǎo méi 士多啤梨 si do be lei
pineapple 菠萝 bō luó 鳳梨 fung lei
bus 公交车 gōng jiāo chē 巴士 baa si

To conclude, learning the simplified Chinese (with less strokes) is easier than learning traditional Chinese. But traditional Chinese is more original to Chinese ancient culture. It depends on one's interest. No matter which, it's better to start now rather than later.

Further reading:
Bullet Train from Beijing to Shanghai: Timetable, Tickets, Prices
China Entry and Travel Restrictions in 2021
Baggage Rules of China Rail