I've heard that using "should" makes a sentence sound more feminine. For example, "What should I do?" Is this true? If so, can you give me an explanation? Thank you in advance.
Differences between male and female speech patterns do exist in English, but they may often be the product of learned differences in status and power, in terms both of cultural biases and of differences in how accustomed the men versus the women in a particular context have become with their actual status and power (e.g., if the women are more likely than the men to have come into positions of power recently, due to rapid changes in cultural biases in this respect, then they may retain habits of speech that reveal their prior status as people without status or power). Peter Kunsmann provides a thorough explanation of this view, along with several examples. The use of the qualifier should would fall into the same category as downtoning, which may involve the use of tag questions (i.e., confirmation-seeking interrogative clauses after statements whose validity is self-evident). If women implicitly seek assurance of their decisions due to cultural learning more often than men do, then they will ask what they should do (i.e., frame a decision normatively) more often than men will under the same conditions.
I'd like to add that there is more to this issue than the question of power and social status. This topic has been extensively researched, and also re-examined by feminist theorists. Here is one example of an interesting paper on the subject: http://www.stanford.edu/~eckert/PDF/CameronTags.pdf, but there are many more.
One alternative explanation for the different language used by women can be seen as related to the cultural and evolutionary need for co-operation. Tag questions, for example, used to be seen as signifying uncertainty or weakness but, in actual fact, could be serving a social purpose- asking someone to agree with your statement can create a social bond, and spark further conversation. Therefore if a woman says 'it's a hot day, isn't it?', they are not asking for confirmation that the day is hot, but are inviting a response, which could encourage the other person to continue the conversation.
If it is true that words such as 'should' are used more often by women (and I am not certain that this is so) then there may be a similar alternative explanation available.
Please be aware that it is very contentious to label such words as 'feminine' or 'masculine'. Gender is a very complex issue and is not the sole factor determining language use. Also the boundaries of gender are far from clear cut, which is why it makes it very difficult to talk about the language that men or women use as a whole.