Deloitte psychometric test comes in form of GeneSys Online IRT3 questionnaire, an online test similar to SHL test format. It consists of 3 primary sections: numerical, verbal, and abstract reasoning.
There's a limited period of time given to complete each sections. The questions might come in form of multiple choice or selection of 2 correlated answers (e.g. synonyms for verbal section)
Verbal Reasoning measures basic vocabularies (e.g. synonyms or antonyms), verbal fluency and the ability to reason using words.
Numerical Reasoning measures the ability to use numbers in a logical, efficient way. It involves basic maths / quants.
Abstract Reasoning measures the ability to understand abstract logical problems and use new information outside the range of prior experience, e.g. abstract shape tests.
Best way to prepare is to utilize SHL practice tests available online or psychometric test examples. The following link can be used for one of your practice round.
Hope it helps.