Mandarin was the first foreign language I studied; I thought it would be immensely difficult, but it turned out to to be the fairly painless. I thought Italian, my last language, would be easy and it turned out to be a real bitch. The reason being that Chinese grammar is remarkably simple: you only have a few verb tenses which are all formed in the same way. On the other hand, Italian, like most European languages, has an incredibly complex grammar with each verb declined into four distinct moods (indicative, subjunctive, conditional, imperative) with each mood having anywhere from 2 to 8 different tenses, many of which are irregular. To make matters worse, each noun has a gender that must always be remembered because of its effect on modifiers. The form of half the words in an average Italian sentence will vary depending on grammatical function.
To anyone used to the complexity of European languages, Chinese has no grammar to speak of; everything is determined by word order and the word order is similar to English. I understand that Chinese students receive very little instruction in grammar, whereas in the West, grammar is hammered into us almost every year of secondary school.
There is a necessary technique to learning a foreign language. Speaking a language is a behavior, an action, something you do. You can't learn to speak a new language only browsing websites, reading books, or sitting passively in class, any more than you can learn to play tennis or ride a bike by watching a video. That is why all these expats living in HK, Japan, etc. never learn to speak the local language in spite of hearing it spoken all around them for 30 yrs. You can only acquire these skills by actually doing them, and because language is a tremendously complex behavior, it takes a LOT of time and practice. That said, anyone can pick up a language if you go about it in the proper way, but most don't, get discouraged and give up.
I had 3 years of intense college-level instruction in the States before moving to Taiwan, but when I arrived in Taiwan, in spite of knowing the proper Chinese terms for things like 'industrialization' and 'consumer', I didn't understand what people were saying when they asked me simple things like if I'd eaten yet. After 6 mths in Taiwan, I learned far more than in those 3 yrs in the States with professional teachers, and I learned it just chatting with Chinese friends. It is instructive to note here that the foreign students who studied with me in Taiwan can be divided into two groups: one group lived among the Chinese, using Chinese, and picked up the language quickly; the other group lived in apts with 4 or 5 other English-speaking foreigners and found GFs/BFs who also spoke English - these people never learned to speak Chinese well, and after 2 yrs the difference between the two groups was night and day.
If you can already read Chinese, these two websites provide useful tools for learning to speak Mandarin.
http://www.pthxx.com/index.html
http://pth.linqi.org/pyzd_biaozhu.html
