The phrase ‘Я должна посмотреть мое расписание‘(‘I need to look at my schedule’) you come across the word ‘должна’ which in this context carries the meaning of necessity. In Russian it is not a verb, but it is a short form adjective which has only one case, the nominative and four endings respectively for masculine, feminine, neuter and plural.
The possessive modifier, which must be expressed in English, may be replaced by another construction or omitted in Russian when the implication is obvious, e.g. ‘Я спрошу жену‘ (‘I will ask (my) wife’). English speakers often forget to use свой where it is obligatory. Study carefully the rules on the use of cвой, своя, свое, свои, since a serious misunderstanding may result. Cвой is obligatory in the 3rd person, cf.: He loves his wife can be rendered as ‘Он любит свою (his own wife) жену‘ or ‘Он любит его (someone else’s wife) жену ‘ With the first and second persons, singular and plural, the use of свой optional as in ‘Я должна посмотреть мое расписание’